Well, from what I remember of the canon explanation of metamorphmagi, they seem to be like a "super-animagus", not being restricted to only one alternate form, and also able to alter their human appearance, something ordinary animagi seem unable to do (else Peter Pettigrew wouldn't have a bald spot!), so to my mind, it seems like they can take on the appearance of almost any living creature, wolf included, if they had a mind to.
So I guess that means Teddy could choose to be a wolf animagus even if he isn't a werewolf, then go back to blue-haired human appearance before becoming a pink butterfly, if that's what he was in the mood for. Or morph into female form, at any apparent age, young or old, once he'd learned how to pull off the transformation.
No wonder Nymphadora became an Auror -- it's a terribly useful talent for a detective.