W2R
Moderator Emeritus
I think "rich" at any stage of life is where you have enough money (since OP wanted to limit this to the $$ factor) to live a life you are content with.
I think you nailed it. Being rich is related more to contentment than to the number of dollars possessed.
"My greatest skill is to want but little." - - H. Thoreau, in Walden
There you go. IMO, Thoreau was really rich! I haven't attained sufficient detachment from material things to be as rich as Thoreau, but at least I am basically content and not at all consumed with longing for things that I cannot afford.