Young looks like a kid playing with grownups. It sounds mean to say, but good lord the kid is going to get broken in half out there. His neck and arms make him look like he's 14.
Couple that with a below average arm strength and it's hopeless. By all accounts he seems like a great guy, smart, hard worker, etc. But he is just plain too small to be an NFL QB.
For reference, Tua is a few inches taller and outweighs Young by 20 pounds.