I know it’s a at best a useless mindset, as nothing will make me somehow magically get a new chance at those years. But it’s still a strong feeling and it’s still there.
I’m doing my best to push through it, I’m out there talking to people, but there’s usually a point where we are sharing personal anecdotes and I just feel my stomach tightening, as I barely have any of those. I have no experiences which means I have no identity which means I am uninteresting.
Assuming you're talking about people traveling and dating and doing stuff with friends in their 20s while you hung out indoors on the computer or something:
I've experienced this with shorter periods of time (on the scale of a year or so) and the main way to move past them is to actually change your life in the way you want. If you're still in the period/mode of doing nothing then you stay stuck worrying about it. If you change your life and start doing things you don't worry about it so much, it just recedes into this amorphous time in the past when nothing happened. Life can be quite long. Are you changing your life to experience those things you want to experience now?
If you'd like some solidarity of experience from another group outside the norm, look up queer temporality.