My older DS had just turned 13 back in May 2001 when we were staying at the Grand Floridian. We did let him get his own water mouse, BUT I also rented one and was out there at the same time he was. Make sure to stress to him that these are NOT "rides", they could, in the wrong situation, kill someone, if used improperly.
Which resort are you staying at? Supposedly the water mice at the moderates are slower because you can only drive them in the smaller lakes at each resort. We were at the Grand Floridian which is on the large lake that also goes to the Contemporary and the Polynesian resort. In my opinion, these water mice were NOT slow. LOL
As long as you feel that your nephew would be careful and not try to speed or show off, and is mature enough, I think he'd be OK. Like Kimberle said, could an adult also rent a water mouse and be there out on the water at the same time?? This way he's not really out there on his own.
By the way, I have a couple of pictures of the water mice on my web sites. Click below on my "family vacations" link. There are pictures of us in the watermice on the "Grand Floridian" page, then I have a couple of pictures of them on my "CBR February 2002" page.
Have fun!
