Directed at Narcberry, although I now realise you are not necessarily quoting from the BNP website. It seems to be a more common argument than I had thought.
Anyway, unless you can talk to animals it's hard to argue bestiality is consentual. Paedophilia is wrong because children are not old enough to feel sexually attracted to anyone, therefore they are being abused for pleasure by an adult. In the case of teenagers, they are biologically old enough but, just as teenagers can biologically drink, smoke, and possibly drive, society sets age limits on these things.