[Farmer]

The physical and cognitive development of most 12 year olds is significantly less than an adult. Whilst there are 12 years olds with are intellectually advanced, the baseline will be quite a bit lower, and even an athletic 12 year old will be significantly less physically capable, in all three attributes by comparison. But IQ is one you could allow to be further above baseline.

There's no reason they can't have disadvantages, in fact, they surely will if they are being played in a setting where they interact with adults, over and above those any individual might have. They're probably not going to have things like lechery (and even if a 12 year old did, I think most people would not want to be role playing it for obvious reasons). But poor eyesight, reduced legal rights, enemies, senses of duty, actual duties, various ailments, etc., etc.