I agree. During the early part of your life, there is so much potential, so many new and different things to experience for the first time, you're generally healthier, have fewer responsibilities, just generally have more life in front of you.
I'm not saying it's impossible to experience new things as you get older, but the older you get, the more doors close.
I'm early 40s, I've done university, done carefree 20s life (going out, travelling, marathon etc), done wedding and marriage, done children, done buying first (and second) homes. There are no real 'big milestones' left.
Career-wise, again not impossible to change, but I'm in a job that I sort of fell into, it's okay, but works around the children, not badly paid... Even though there's other things I might want to do, I can't really anymore, not without compromising on pay and/or flexibility.
Tbh, I've always been a pessimist (though, I prefer realist, and actually I think there has been some research to show that pessimists are actually just realistic, whereas optimists have their heads in the clouds 😁)
And obviously being alive is the better position to be in, but when you cross that mid-point line, there isn't a huge amount left to look forward to. Deteriorating health and hopefully eventual retirement.