My dd is 15 and her bf is 16 so they don't have that big of an age gap. However I would be more considered about the kid more than the age. If I liked the boy and he was 4 yrs older I think I would be ok with that.
My dd just got hers a month ago, it's scarey belive me. At first she couldn't understand why I wouldn't let her have the radio on or drink her coffee when she was driving hahaha. Things have gotten better though and she will hopefully get her license when she turns 16 in January.