I am in my 40s. I was a musician in my 20s. I got to do a lot of fun things in my 20s (lots of performances, touring, travel, staying out late, practicing all day) that I would not want to do or be able to do in my 40s. You have so much more energy in your 20s and are so ready and willing to soak up new and different experiences than when you are in your 40s.
Plus, the odds of actually being able to retire early or have a light enough schedule to be able to travel and do different things in your 40s and 50s is very, very low. Most people will either not make that kind of money or won't let themselves walk away from their careers even though they could financially.
As long as people in their 20s are actually doing something they love, not hanging out playing video games or partying on their parents' dime, there is no better time in someone's life to pursue a crazy dream, even if the chances of success are next to zero.