Hi Elfish,
I sail the Blade together with my girlfriend and it's an excellent boat for us. If your interested in racing, F16's are lovely machines. We really give the F18 a hard time.
Also one-up I really like the boat. I think it's difficult to be too heavy one-up. I weigh about 72kg and have to depower from F3 onwards.
Personally I started sailing a Nacra 5.0 (as skipper) when I was 14, an F16 shouldn't be a problem either and much more fun for a kid because everything is just a little less fysical.