Need a good comeback for "aren't you a little old to be playing with dolls?"

I would say "aren't you too old to watch TV and not read a bibliography?"

Mind you, you're 20, not 10, by roughly age 13 or 14 you should have gotten rid of your toys by now and learned to do something else to illicit play with others. By age 24-30 you're supposed to have a nuclear family and be married.