People living off a McDonald's salary are already used to living a simple life with few luxuries, so as long as he doesnt buy anything too extravagant, like a 300k house, or 100k car, he can easily live off this for at the very least 10 years, even longer if he's from a small southern/midwest town where everything is cheaper than say NYC, Cali, Chicago, etc.
I just calculated my bills + food budget for 10 years and it equals 80k so

I'd be quitting my job too, I do have a roommate I split everything 50/50 with tho so if I lived alone or with a family I might not quit
