If he's your oldest, and you haven't been through the college process before, it's never too early to begin. Grab a few reputable college books or use some on-line sites to start your preparation. Set up an appointment with the school guidence counselor - he/she will be able to set you in the right direction.
Quite obviously, the better the baseball skills AND the better the academics, the more options will emerge. On the academic side, course rigor and grades, and scores are the critical data points. The goal is fulfilling his academic potential - so, if there are any learning issues, get help; sit on him academically, get to know his teachers, monitor his progress on-line (most schools have on-line systems), accept nothing less in the classroom than you'd accept on the field.
Start visiting local colleges and - on vacations - nearby colleges. Doesn't matter initially if those schools would be acceptable - you're looking at things like size, facilities, majors, etc. It can be a formidable task which can't really be rushed (because there is just so much info to absorb). Go to a bunch of local college games (all divisions and JUCOS) to get a feel for the levels of play.
You'll find that at the same time as recruiting is heating up, the standardized tests are scheduled. So, try to get those tests out of the way (and if you can, pay for a reputable test prep service) as soon as he can test successfully.
One other variable will be college cost and the intersection with family finance. Often, finances are a limiting variable, so try to peer into the future and decide your limits (if any) and what steps you could take to make college more affordable.
You'll get plenty of good baseball advice here, but looking backwards (to us) the academics were as important as baseball in the short run (through college); and THE MOST CRITICAL element in the long run (through the 20s and, hopefully, beyond).