When is it okay to have a job full time? The answers should be the same. The only reason to go to college or university is to learn a trade or profession. If all you want is knowledge, read a book.
The question one might ask is when should one start to work full time (in the past many people would get married and then worry about supporting themselves, but I suspect than since the crash five years ago increasing numbers of young men are more concerned about finding parnassah than finding a wife – in part since jobs are scarce and unmarried frum girls aren’t).