I started getting it as a teen, in addition to clothing. When my family started noticing that I didn't seem very enthusiastic about the clothing, would not wear it, or they had to keep returning it because it didn't fit or flatter me, then they started giving me cash only (inside a personal Christmas card they'd write a message in), or cash (again, inside a card) and costume jewelry, maybe cash and a purse -- stuff that doesn't require trying on. I love getting cash or gift cards, it gives me the freedom to buy something I need (shoes, jeans, underwear, groceries, gas, paying the car mechanic) without feeling pressured to wear something someone got me and I disliked, or having more clothing than I need at the time. I may be more pressed to pay $500 to the mechanic and a $100 gift card would help a lot in that respect, rather than having a fourth pair of black shoes.
We all give each other cash in my family, or gift certificates for those reasons. It's so much easier and no one wants to go on NYE weekend when the malls are bursting and stand for 1-2 hours in line to return something or exchange it, and then have to go yet again to take it back because it didn't fit or it was not liked. My kiddo (10 years old) has too many toys and everything she could possibly need and is getting older. She is fine with getting an "experience" (aka, a vacation/road trip to a fun place) as a holiday gift, rather than toys, though she also likes getting new 3DS games or XBox games. She loves Legos and has plenty, so this year I am surprising her with a trip to Legoland Florida and some other fun stops like ice tubing at a hotel, and visiting some holiday attractions.
Perhaps your son would also like an experience. A cruise perhaps? Going to an aquarium and having an up close sea creature experience (like swimming with the dolphins)? A road trip somewhere fun? An amusement park? Front row tickets to a band or sports team he likes? I guess that is similar to giving cash (no unwrapping needed), but at least there may still be some mystery as to what type of experience you're choosing to gift to him every year. My mom gets my daughter clothes, because she is constantly outgrowing her outfits and my daughter's still at an age where she is okay with wearing whatever we pick for her (always useful, play outfits and sneakers, rather than frilly dresses she'd hardly ever wear).