A old family friend always said that 18 was a good time for a proper knife. In modern times they consider graduating high school when to give a good knife.
I like the suggestions though.
Since he is a mechanic, I would consider finding out if he needs some tool or would appreciate a gift card for the place he buys them. A lot of mechanics own all of their tools and they move with them where ever they go. A proper tool can last a decade or more and really good ones have lifetime warranties.
That's a great idea. Or spare batteries for his chosen brand of power tools. Can never have enough.