It depends on what kind of kid he is. My older daughter (now 24) went to a Warped Tour event when she was 17. It was hot out, she was with friends, and it was basically her first concert. She did fine and had a great time. I still hear stories about it to this day.
In fact, she and her boyfriend are taking my younger daughter and her best friend (both 14) to the Warped Tour this July in Chicago.
(Check out the Warped Tour website. If you do decide you don't want to just send him there, they have activities for parents, and a tent where parents can cool off, use their computers, etc., and talk to other parents without actually hanging with their kids. If my older wasn't taking my younger, that's what I would be doing this year.)
The concerts are well managed, lots of security, plenty of water if it's hot and lots and lots of bands. My younger daughter loves music and unknown bands and is really looking forward to it.
Yes, there can be trouble at these kinds of events. There can be trouble at the mall! But if your son likes music and has a good head on his shoulders (and isn't known for getting into trouble) I think you're ok. But it's a total judgment call on your part.