Pretty much everyone figures out how to actually socialize, maintain relationships, have new relationships, improve them, and date at high school, MAYBE college at the latest. I'm 30, almost 31. Did I miss the boat on learning that and having a semblance of happiness in my life, and there's no going back.
I've tried it all. I've tried social hobbies, I've tried going out, I've tried putting myself out there. The basics of social skills elude me. I am, at best, a filler friend. I can't see myself being any more than that, and I think it's too late for me to get better.
I think I doomed myself to a life of loneliness, all because of the bad choices I made. The only possible hope I can have is maybe reincarnation is real and I can suck less in the next life.
I think you're getting bogged down by what I call narrativistic inertia (there's probably a better term for it). We exist in a complex world, inundated by a constant stream of data, and we make sense of it through associations and patterns and selections that coalesce into a sort of narrative that we use to understand everything and ourselves. These narratives are both useful and limiting. Useful in that they allow us to make some sort of sense out of chaos, but limiting in that we're necessarily ignoring or de-emphasizing a large portion of the data presented to us, or arbitrarily associating some data points to other data points. It's tremendously helpful to identify when an emphasis or association isn't serving us so we can attempt to adjust the narrative we're using to understand ourselves. Psychedelics may be useful here.
Unnecessarily long-winded intro aside, the idea that it's "too late" to do something or become someone is a restrictive, self-producing narrative. People develop new skills and relationships throughout their entire life. A person who wasn't able to follow a mythical narrative of social interaction throughout early life isn't just done, there's no actual ship that's sailed, no barrier for entry that only allows 20-somethings to socialize.
That's not to ignore the underlying material factors that make forming relationships difficult. Capitalist alienation, consumerization of identities, enclosure of public spaces, interpersonal difficulties all increase the energy required to form connections with people. But a defeatist ideal has no chance of influencing the material conditions for the better.
The reality is no one actually has it "figured out" by high school, college, or any age. We all strive towards an unachievable pure connection with others, never quite succeeding but potentially having some cool experiences along the way.
This is all abstract and big-picture, the little every-day strategies and skills are something that must also be examined. But in my personal experience at least, a defeatist self-narrative is a difficult foundation to build from.