The most optimal thing to do in our world is to pick an age, say, 60, and until your 60th birthday, maximize your suffering via frugality to just under the tolerable limit so as to maximize your potential for compound interest. This leaves you with the most freedom and opportunity during the most fun part of your life, when you no longer have to sell your labor and can do whatever you want.
Within our current model, trying to slip in bits of fun through spending money before that age is getting a poor return: you're trading vacation time, which you could instead barter for more money on retirement, and you're carrying with you a bit of suffering because you have to worry about going back to work. The best thing to do is just push it all until retirement.
The limit of human suffering before suicide frequently happens is apparently quite high, so, you can really stretch yourself out here. Live in your car in the Walmart parking lot, eat beans and rice. You maybe trade a bit of the compound earnings to establish certain time constrained things you want to cash in on at 60 like having a partner or kids, but beyond that, maximize that compound interest!
I hope it's obvious that this is a criticism. It's just, the more I think about it, the more this seems the selective pressure and incentives in our society are set up. Mostly I think it's insane that we both have an idea of "retirement" and also that we set it at an age where a significant portion of the population won't make it, and for those that do, a significant portion will get to enjoy five years of it, and for the remainder, health is bad enough that maximum enjoyment isn't possible anyway.