T.V.
A.,
You made the right decision. Minors have no business going away over night without an adult present (other then sleep overs where there would still be an adult present). An exception might be if you know the other family and you know the other kid very well. As far as groups going to the beach with mixed ages, that is asking for trouble.
Many of us think when a kid gets to be 15, 16, 17 that is OK to leave them at the house over the weekend. I disagree because even the best kids, the smartest kids like the idea of having a little party while mom and dad are "out of the house".
He will be 18 in on the way to college soon enough. Just the time between now and then, he will be better able to make good decisions.
A example of letting a kid go on vacation with other kids and no supervision is Natalie Holloway. She never came back.
Lastly, let me add, I had a pretty good kid too, what I use to tell him when he would say, "Mom, you can trust me"....I would say , "Paul, I do trust YOU, it's the people I don't know that I can't trust"!
Blessings......