The “Birth Order Dating Theory” Just Explained Why I Should Never Date an Older Sibling

Back in December, I was on my way to meet ‘Ryan’ for drinks in Tribeca. We matched on Hinge two days prior, and I appreciated how quick he was to set and plan a date. When I walked into this dimly lit cocktail bar, however, Ryan was standing with his arms crossed at the hostess stand. “There’s a 15-minute wait,” was the first thing to come out of his mouth. Nice to meet you too, I thought to myself. Clearly, he was annoyed: “What’s the point of making a reservation if they don’t seat you on time?” It was going to be a long night. I nodded contentiously before suggesting that we grab drinks at the bar. (Now I was the one who couldn’t wait for a martini.)

After 15 minutes of mind-numbing small talk, the hostess led us to a table by the bathroom. “Is this the only table that’s available?” Ryan looked at her with a snooty glare. He had to be kidding. I should’ve bit my tongue, but I couldn’t help myself: “We’re fine here,” I told the hostess. Thankfully, she high-tailed it out of there before my date could rebut. And then, once we finally sat down, he shared a tidbit that put everything into perspective: Ah, of course, he was an only child. 

“A firstborn and an only child tend to be a tough match,” explains one TikToker named Caroline in a video. “As two independent people, they like to be in control of things.” Suddenly, the instant friction between me, an older sister, and Ryan, an only child, made perfect sense. “Your birth order may influence your adult relationships because it impacts how you act and perceive things.” And for those who don’t already know where I’m headed, she was explaining the birth order dating theory—a TikTok trend that’s been blowing up lately. 

So below, I tapped a psychologist to see how the Birth Order Theory applies to dating. (Grab your notebooks, older siblings.)

Meet The Expert

Dr. Jennifer Hartstein is a nationally recognized child, adolescent and family psychologist practicing in New York City. She received her BA from George Washington University and worked in two adolescent inpatient units, implementing group therapy programs, before returning to Yeshiva University for her doctorate in School-Child Clinical Psychology. Today, she’s a frequent contributor to news programs, including NBC’s TODAY Show and CBS’ The Early Show and the author of Princess Recovery: A How-to Guide for Empowering Girls to Create Their Own Happily Ever Afters.

Because eldest siblings often lose the full attention of their parents within the first four years of life—aka before they feel fully secure—they become highly attuned to their surroundings. This stems from anxiety that they’ll be replaced or forgotten; they assume a perfectionist mindset to help ward off rejection (which can also lead to difficulty managing criticism). At the same time, however, this is why they become excellent caretakers who can ‘read a room.’ Many studies have found that firstborns start talking earlier, causing them to be more responsible, achievement-oriented and successful than their siblings. In fact, 21 of the first 23 American astronauts and 52 percent of presidents were firstborn or only children. 

Unlike their older and younger siblings, middleborns aren’t used to being the center of attention. This, in turn, is what leads to their adaptable nature—they learn how to compromise in a wide range of social situations. (It’s also why they’re usually agreeable and get along well with others.) Contrastingly, this inclination to compromise can also be to their detriment. Middle children tend to struggle with identifying clear goals and following through. They can also feel overshadowed by the needs of their siblings—especially if they have more than two brothers/sisters. According to Hartstein, this is why middleborns might be the first siblings to move out: They’re looking for attention they can’t find at home. 

More often than not, parents place looser expectations on the youngest—they have more wiggle room to take risks (aka, f*ck up). This is why lastborns might seem outgoing, rebellious and unconcerned with perfection: They were less likely to get in trouble. By the same token, it also meant they had less pressure to succeed. If they wanted to get their parent’s attention, they had to stand out—maybe by making controversial decisions and questionable life choices (their siblings didn’t make). Plus, since lastborns are used to being taken care of, they can feel especially let down when someone isn’t there for them. They can be charming and lighthearted when things are good but equally combative when things don’t go their way. 

Finally, Hartstein mentions how parents place “all of their eggs in one basket” with the only child. In most cases, that means they had higher expectations to succeed in school or sports—all eyes were on them. Plus, without the competition or support of siblings, only children can become extremely self-confident and independent. They approach life through a more solitary lens, often causing them to set unrealistic expectations. (They also have a hard time tolerating any kind of disorder.) This, coupled with the pressure to succeed at the highest-performing level, is why only children might seem obsessed with perfection. 

So, if we take this birth order theory in mind, which siblings are most compatible? “Firstborns and lastborns are a good match,” Hartstein starts. “The idea of opposites attracting definitely rings true here.” This is because firstborns are used to a) taking care of others, b) being in control and c) creating scenarios for success. Lastborns, on the other hand, feel right at home when they’re dependent—they’re actually looking for a partner who can take care of them. Not to mention that lastborns are usually charming and charismatic with a lighthearted sense of adventure. “This is why they balance each other out,” Hartstein summarizes. She also adds how “only children and lastborns balance each other out as well.” This has to do with the fact that firstborns and only children are cut from the same cloth: self-reliant and expected to succeed. Meanwhile, the younger sibling brings liveliness and creativity to the relationship. Lastborns can help a more responsible (tightly wound) partner loosen up. 

She continues: “Firstborns do well with middle children” because the latter tend to be easygoing and flexible. While the firstborn is a firecracker when it comes to making plans and putting them into action, they’re not always great at relinquishing control. Luckily, middleborns are less inclined to have strong opinions—and even when they do, they probably won’t share them. So long as their partner is happy, and they can help keep them calm, the middle sibling is content. To that end, because middleborns are innately adaptable and agreeable, it’s easy for them to make friends in new social settings. If the firstborn is planning a big trip, or they need an impressive date to a gala, the middle child is a perfect partner to tag along (without interrupting the eldest’s meticulously crafted itinerary). 

“Two firstborns in a relationship may have trouble compromising,” says the doc. Naturally, this is because both partners are used to taking the lead—and neither is accustomed to letting go of control. This power struggle is also why “firstborns and only children tend to have difficulties in a relationship.” Again, you have two opinionated, self-reliant people who find it hard to reach common ground. Per Hartstein, “It’s important to stop and figure out how to navigate this potential problem—negotiation is key.” Essentially, she says that the only way a firstborn/only child dynamic can work is if each individual respects and understands where the other is coming from. “Figure out where each of your strengths lie and learn to compromise,” she explains. It’s also worth mentioning that, in order to satisfy their need for perfection, firstborns and only children should find a hobby or something they excel at outside of the relationship. It could be anything from coaching Little League to starting a new business venture—so long as they have a place where they can call the shots. 

“A match-up of two lastborns can also be problematic,” Hartstein continues. While younger siblings might approach life with a ‘fly by the seat of my pants’ attitude, they also tend to fall short in the planning department. This can make for a chaotic pairing since neither lastborn knows how to properly care for the other (let alone themselves). “It’s important to learn organizational and planning skills together, so projects can be completed and the mundane things in life are addressed.” Translation? They’ll need a well-synced calendar system with bill reminders if they want to avoid being evicted.

At this point, you might be worried: I’m a firstborn, my boyfriend’s a firstborn…we’ll never make it. Not the case. As Hartstein mentioned above, there are ways to work around the power struggle if both partners are willing to compromise. (And who would be better suited to problem solve than two perfectionists who strive to succeed?) If you can reach an agreement on which partner takes charge where—and learn to sit back and relax while they handle something—you two can take over the world. And on that note, youngest siblings are just as likely to succeed as a couple: nothing a good planner and Marie Kondo course can’t fix.

The Bottom Line: I’m treating the Birth Order Theory like I do zodiac compatibility. On one hand, it opened my eyes to personality traits I didn’t know I had. This is useful because a) it helps me better understand myself and b) it gives me ammunition for the next fight with my younger sister. (Kidding, but not really—the kid had it easy). But of course, an abstract theory can’t speak to the sum of my personality. While I might be categorized as a caring older sister, I was also irresponsible enough to throw wild parties in high school and drive my Dad’s Jeep without a license. If I were you, I’d take what resonates, forget what doesn’t, and do the same for (whichever sibling) you’re dating.