What's the right age for sleepovers?
I remember my first sleepover. Not a lot of sleep happened. A lot of Goldeneye happened on the Nintendo 64, that's for certain. I was about 10-years-old when I had my first sleepover but, really, the suitable age depends on the kids involved – and the parents taking responsibility for them.
There's some good rules of thumb, like if they're reasonably good at falling asleep on their own – and don't need to be reassured by their parents – at home, they should do all right at someone else's house too. If they've already had a taste of indepenence, they'll easily keep it up.
Something else to bear in mind is the aftermath.
If they've stayed over with some fairly easy-going parents (or if they're as sneaky as me and my friends were, with the volume turned down and being very careful not to make any noise with the N64 controllers), then you could find the next night that they're a bit reluctant to go to bed at the bedtime you set. After all, it was different at Timmy's house! They stayed up all night eating sweets and watching Despicable Me 2!
Sleepovers aren't quite a military operation, but it might be best to do some recon beforehand.