Boys - Clothes - Help! Helping My Man's "Style."?

My man is 20, turning 21 in a month. He has always worn kind of "teen" clothes - hooded sweatshirts and t-shirts with patterns, skate shoes, typically DC Shoe Company. I love him no matter what clothes he wears, but he's always asking my opinion on that kind of stuff, saying "do you like this outfit or that one?" So I thought for Christmas one thing I could do was to buy him some more adult clothes. I find sweaters very attractive on men. However, I know that is a huge leap from wearing name brand t-shirts to sweaters and dress shoes. Is this a bad idea?