I believe that Luke turns 17 on 21st Jan.
He's clearly very mature for his age, and I don't mean the way he looks. He's performing at an amazing level at the most prestigious darts tournament; players three times his age crumble under that kind of pressure. I can't think of any other sport where the spectators are wearing fancy dress and screaming/singing while you're trying to concentrate.
When I was his age (I'm old, so this was last century) I can't think of a single friend whose boyfriend wasn't at least 4 years older. At 16 we could get into nightclubs easily, whereas boys our own age could not. I can't recall a single parent raising concerns.
Luke's got his close family around him; I'm sure they know them both better than anyone and will voice any concerns.
Perhaps again it's my age, but regardless of which sex is older, I can't see an issue if they meet when they are both over the legal age of consent.
Good luck to Luke!