Why is 20s soo fixated on?

So I’m in my early 20s and although I’m no where I want to be, I do think I’d be a lot happier if I had 2 things but that’s not the point of this because we all want things we don’t have.
Thing is I just want to understand why people are so fixated on their 20s being the best years of their lives?

Like there’s so much scaremongering towards being 25, 29 and ultimately being 30.
Yes we all don’t get to live till we’re 90 but there’s still 30s,40s,50s and so on.

Perhaps it’s coming from the pov that we’re supposed to have kids in our 30s, or the fact that society has deemed us no longer “young”?
Like people put limitations on themselves like because you’re now 30 you can’t go clubbing ?

It’s probably cause everyone is on different paths and comparison is a bitch.

Anyways just want to hear people’s thoughts. It makes me panic sometimes but I guess if we were all rich we probably wouldn’t really worry about our ages.