Speaking of which! (now that my borrowed internets loaded this page after 45 min of loadtime, I kid you not)
People with concepts that don't have outright mutations listed, but want their kid to be included in the plotstuffs: I might make physical adjustments and create mutations, if you did not provide any. I'm just warning you in advance that if you expect your kid to be completely proportionate and such, you're probably in for a bit of a surprise.
If anyone is super attached to their concept down to the T of what you described, shoot me a PM; I'll make your teen into a regular Hiccup instead, so you can preserve your vision. Just be warned that you would no longer be involved in the mutation plotline that way. 3nodding