Impuberal is an adjective that means ‘having not reached puberty’ or ‘immature.’ 

The Latin word pubertas (poo BURR toss) means ‘the age of maturity or adulthood.’ Its young English descendant, puberty means the same. The addition of the prefix I-M, meaning ‘not,’ gives us a word that means ‘not yet mature.’ Example:

All those impuberal jokes at our workplace get to be a bit annoying after a while. There are only so many whoopie cushions a person can endure from his co-workers before reaching the breaking point.