L.A.
My nephew is like this, but they know what they can handle. Remember these are kids that have a lot of energy, lots!
They get up early take the boat out, go skiing all day, than do these sleep overs at night.. And the continue over and over.
He is the quarterback this year and has lots of strength training every morning, goes to the lake all day and then goes out for a few hours at night..all of this time eating the largest quantities of food you can imagine. And then he makes sure he gets enough sleep.
Mention to them you are wondering about the amount of actual sleep they are getting. During the summer there are lots more sleep overs even when he was on select teams and traveling around the country, all of that swimming in the hotel pools having to catch sleep in vans and cars. Just by mentioning it to your son, will give your son something to consider.
But mom, he is now old enough to decide his priorities and take the consequences. You can state your observations, your opinions, and your concerns, but it is time for him to make these choices and then learn his limits.
If this is the worst thing you are worried about, you have done an excellent job as a parent.