How old is too old to be living (back) with your parents?

The only friends of mine who aren't in my situation are the friends in relationships.

Where I live, you need at least two incomes to justify renting (owning is now a pipe dream). A single bedroom, communal living space, in the city is $2400 a month. An hour outside of the city, a 1 bedroom 1 bath is $1850.

What even.