I always had the 36 figure in my head: "I will enjoy life as much as possible to 36 and then calm down". Unfortunately (or fortunately depending on how you look at it) I have trained my brain to enjoy life to its fullest as much as possible, I can't snap out of it.
I suspect that these people who forego living to put cash to one side with the premise that in the future they'll be able to live the good life will find they are mentally unable to make that switch too.
I am now 44 and can say that my 20s were amazing, my 30s even better (because I understood myself much more), my 40s have been pretty good, but it's clear I am slowing down a touch - the motivations to live every moment are fighting with the slight loss in energy as I age.
Why anybody would think it makes sense to put the best years of their lives (in terms of physical fitness) to one side in the promise of some later payoff is beyond me.