I believe that a quad's capability should always exceed the rider's skill level. This will give the rider's skill room to grow and not be held back because of the limits of the quad. That said... skill and age are NOT the same thing and therefore when a kid is ready for a larger quad (mo' power) should not be dependent on age. Some states may have laws regarding at what age a kid can ride a full size quad, California doesn't. California does have a law about being able to reach all controls... being able to use the clutch in a full right turn and so forth... A tall 14yo may be able to ride a full size quad, but a short 16yo may be screwed. A kid's time riding does not necessarily equate to skill... A kid riding for 2 years just putting around on the farm will not get the same experience as another kid riding for 2 years doing MX. My 2 nieces 10yo and 15yo currently ride a 250ex and a 450r... to keep up with dad... their pictures are in my garage pics. I think that most states reguire some kind of safety certificate for riders under 18, but as far as I'm concerned... the sticker on your quad about riders under 16 and what it says in the manual don't really mean shit.