Nah, man, the people saying we all have too limited of a perspective and draw conclusions too readily are right. Every possible course of action involves risk and uncertain outcomes. My parents married at 18 and 20, a few weeks after my mom graduated high school. They're still together in their mid-60s, have a disturbingly great and loud sex life, are the epitome of lifelong friends. I tried to marry at 21 and my first wife descended into a drug habit, destroyed our apartment and got the lease terminated, was committed to a psych ward and left me temporarily homeless. That didn't work out, though arguably, maybe it could have. She'd be in her 50s now and I don't know if she's even still alive, but last I had contact with her a decade ago, she seemed to be doing well. I finally married someone that stuck later on and we're past a decade, inside of two still, and she's been in the ICU seemingly inches from death twice in that time due to alcoholism, but I guess it's just different being older, more experienced, somehow able to deal with that and not have your entire life necessarily spiral into complete chaos.
My actual first girlfriend from high school isn't a person I kept in touch with, but from what I saw of the 20 year reunion a while back, she got really fat, became a bizarrely hardcore religious fundamentalist, and was extremely into Trump. I can't imagine a world in which a marriage with her would have worked. I don't see how you can possibly hope to imagine what a person might become decades later when you're 16.
I agree entirely with you about growing together through challenges and creating deep bonds through shared experiences. I'm just not sure why you think those don't continue happening past childhood. My 30s were by far the toughest decade due to unexpected physical challenges from spinal degeneration, and having someone there for it made all the difference in the world. I will love and cherish her forever for that, no matter what else happens. I didn't need to know her in high school for that to be possible.
And all the breakups of the past didn't take a toll on me. They taught me that loss isn't really that big of a deal. Life doesn't have to be constant and predictable. People come and go. Jobs come and go. The world turns, life goes on, and I'll be fine. Some other opportunity always comes along. More often than not, each one turns out to be better than the last one. I certainly don't want my wife to die and have no intention of ever divorcing her, but if something does happen, I have no doubt I'll be fine. Grieve, sure. Be crushed for maybe a year or two. But life is long as fuck and a year or two fades into nothing decades later when you're happy again.