I should point out that it's cheaper to travel when young: Back then I stayed in a tent in the desert and in a friend's room near Amsterdam. If I did the same trip today, I'd have my family in tow, and would need more comfortable accommodations.
I should also point out that startup equity is not retirement savings. Selling 10% of your equity, investing most of it, and then doing something that you won't be able to do when you're old is a very wise and mature decision.
After 40 you've already made many of your major life decisions - career, partner, education, kids etc. There's less room for new experiences to alter that trajectory meaningfully.
One thing I've also realized through being lucky enough to enjoy some "semi-retirement" between work is having a healthy balance makes me appreciate both work and "leisure" more. It gets pretty boring to go to the beach every day, it turns out. I was itching to get back to building something by the end.
Do you really believe people who have health issues at an early age are simply stupid?
If you can retire at 40 having lived your 20s/30s to the fullest then game on, but it would be crazy to sacrifice that time when you are so free and full of energy otherwise IMHO.
FWIW I am fortunate enough to have really enjoyed by earlier years and be mostly retired in my early 40s.