Let's see... Elves are grown to full stature when they're 50, but they aren't mature until 100 years (so I reckon 100 is about 21 in human years). But during the long years when they look like children, they still also act like children. And yet, they could walk, talk and even sing when they're already 1 years old.
Cute concept, but you'll want to revisit Thranduil's free hand. I'm more goofball than 'shop-jockey but I'm not sure that even an Elven wrist can twist through that many degrees, at least not without getting the elbow involved.
Sorry, I was referring to the way that Thranduil's left hand is drawn- I'm not quite sure what you're going for, but I think you got it on backwards. It looks like we would ordinarily be looking at the back of his hands.