Most adult-at-home children that I know, are there in a companionship or caretaking role.
I've run across several because of the work I'm in, and a more pathetic lot cannot be found. The worst of them was 38 and working as a part time cashier at a gas station/convenience store. Never, ever aspired to anything more.
His mommy took him to appointments because of his DUIs, and, I came to find out, still did his laundry, fixed all his meals, etc.
I don't know who I wanted to smack more, him or the widow.
I've seen girls do it, and some married people regress to it. I call 'em the "wah, wah Moooooooommmmy" crowd.