I don't like the sound of it. The sound of a 14 y/o girl and a 21 y/o guy makes me think of them in potentially unfair ways, but still concerns me.
A 14 year old girl will want to be with him because "He's so mature, he's older! He's got a job, most guys my own age can't even grow facial hair #immature."
A 21 year old guy will want to be with her because "I'm horny and she wants to seem like a grown up, so she'll do it."
Do you or your mother know who he is if you know his age? If so I'd recommend a serious confrontation. Not necessarily to break them up, but rather make sure he's keeping it in his pants under threat of castration.