When would you let your kids boat alone?

OK, maybe I am just a little bored and already thinking of next summer...

But, when would you, or would you, let your kids take your boat out alone?

My son will be 16 next summer and while he won't have permission just yet to take the boat out, it can't be too far away where he will ask.

Scary things is, he got his boating permit when he was 12 (he could legally drive the boat by himself). If we were to have our boat docked at a marina (which we don't) he could have rode his bike to the marina and legally gone out on the lake with all his friends.

I know some folks have lake houses and their kids can probably go out already but this is a big change for me.