Earlier quoted context omitted.
I'm not saying an 18 year couldn't easily live on $100k / year. They certainly can, but you do have expenses besides rent and groceries you know.
I actually don't, those are the only two expenses my family has. Come to think of it those are the only two expenses I've ever had. I guess if we lived in the countryside we'd need a car, so, three expense categories total. But alright, gather all of these other miscellaneous expenses up and take out another $10k per year to cover them. You still have $30,000 left if you're paying $2k a month on rent.
If you have a car, - car insurance - gas - car maintenance costs such as 6 month services