A secured card is the best bet at this age. It's also not a bad thing for him -- if he isn't used to having a credit card, he might lose his mind at the "free money" for a bit (or, say, make poor spending choices while under the influence/out with friends/etc. -- he's a kid, he's going to be stupid once in a while), and so having a secured card will limit any potential damage while he's learning to use this new power.
Be careful about adding him as an authorized user. I understand (though do not know first-hand) that the CC companies are cracking down on how much of a boost this will provide to his credit history. But what I do know first-hand is two things:
1. You will be responsible if he loses his mind (see first point above); and
2. If he's on your CC, your credit limit/balance is imputed to him, which will affect his ability to get his own CC. My DD had a job post-college making around $80K, with zero debt, no negative history, etc. She couldn't get anything but a secured card with a $500 credit limit. Why? She was a AU on one of our CCs, and we have a high credit limit, and the CC companies declared that she already had too much credit available for her salary and refused to extend additional credit to her. (Ironically, that means she has to stay on our card, because a secured card with a $500 credit limit is insufficient to cover any true emergencies, which is precisely why she wanted her own CC in the first place).
