Not all Aries are going to be bold. At least not immediately. Show him you're interested. Aries men and women do not like to chase unless it's for something worthwhile. I'm sure as soon as you give him the ok, he'll be after you. Just let him know that you like him.
He's by calling a lot because he's busy. Aries people can be a little self involved when it comes to work. As long as he's still calling and talking, I wouldn't worry about it. I'm sure he's giving his parents the same kind of "treatment".