17 would mean he's either a junior or a senior in high school. Core (required) courses would probably include English (most likely AP III or IV) and math (placement all depends but likely either pre-calculus, Calculus AB or Calculus BC). If he's a junior history and science classes are probably still required as well. My junior year I took US History and AP Environmental Science, which is not an uncommon path.
There's language requirements to consider. Most high schools ask for 2 years of a language to graduate, some more, some less, but most colleges look for 4 years of a language so if that's where your character is aiming to be after high school I'd probably have him taking a language as well (Spanish, French, Japanese and Latin are pretty commonly taught I believe). Then there are electives.. and don't forget to include a lunch break about halfway through the day! My school had 7 courses a day for 45 minutes each, but lots of schools do a block method instead. Oh, and don't forget to think about how he's getting to and from school. Does he have his own car, ride the bus, walk...?
As to the types of people, usually you can break it up into two general categories -- the kids who want to be there (or at least suck it up) and the kids who don't. It depends on your character's personality as to what types of kids he'd hang out with. The kids who want to be there do exactly what it sounds like they'd do -- attend class, show up on time, do their work, engage in the classroom, etc.. The kids who don't will either sulk at the back of the classroom or sleep, or just skip class entirely to either wander around in the hallways or go outside to smoke weed (or do it in the bathrooms, which is 7 degrees of annoying). That's how things were at my high school anyway.