I get a newsletter from the Berkeley Greater Good Science Center and this is one of their articles:
Happiness is Being Socially Connected
"The upshot of 50 years of happiness research is that the quantity and quality of a person's social connections—friendships, relationships with family members, closeness to neighbors, etc.—is so closely related to well-being and personal happiness the two can practically be equated. People with many friendships are less likely to experience sadness, loneliness, low self-esteem, and problems with eating and sleeping."
That's the crux of the issue I see with both the OP guy's and Grocery Store Guy's decisions to keep living like a college student the rest of their lives (they really have no option by RE'ing that young with that little): after their peers move upward beyond bachelor apartments, I think they're going to end up really isolated. Grocery store guy can probably get away hanging out with the unmarried 20-somethings for a few more years, but once he's in his 40's, he becomes the weird old guy. Meanwhile his middle-aged peers have all moved on with their lives, moved into the suburbs and are raising their families in the usual middle/upper-middle class lifestyle. They will have nothing in common with a middle-aged man still living like a college student in a cheap apartment.
I really think you need to have enough before you RE to at least live the lifestyle of your peers after they get older, so you can still socialize with them and feel connected.