I have zero balance right now. I like to pretend that I'm paying my dues for later in life and it helps me cope with the stress. However, every chance I get that allows me to have free time, I fill with more stuff to do.
Maybe I just like the grind, but I'm always thinking what is this costing me? (Especially since I'm in my later thirties.)
Filling free time isn't a problem maybe. Or, it depends what you fill it with I guess.
Once past 40, you will feel the affects of what you have done prior :)