What does lightest license of a child mean?

This referes to a quote from Charles Dickens' "A Christmas Carol". Witnessing himself at a party as a young man, Scrooge is lamenting to the Ghost of Christmas Past that he didn't allow himself to be young and playful and how he might have won the young lady being described if he had not been so guraded and reserved. He should have granted himself licence (allowed himself) to be young. The lightest licence of a child, rather than the heavy heart and restraint of a bitter old man.