He was 19 in the show. On AWOIAF wiki it says Born in 283 AC and Died in 299 ac. Which makes him younger (16). That's why they keep calling him the young wolf, not because he is 21 or something. But 16 may not be true tho. 19 is still far too young for a guy to become a king. And he still did gud.
And the book robb wasn't blamed by everyone cuz of his actions. The writers kinda tried to make Northmen like impatient traitors.
Ahh man, i miss the young wolf.