What comes next after private pilot license?

After the PPL you have a lot of choices – including the instrument rating, multi-engine rating, complex / high performance endorsement, , tailwheel endorsement, floatplane rating, etc. You do not have to do them in any particular order, although most people tackle the instrument rating next. You may obtain all of these before doing the commercial pilot training, or after. The only limitation is that you must be at least 18 to take the commercial pilot checkride. So, the answer is yes, you can do any or all of these before or while in college, assuming that you will have the time and money. It would take you about a year of training full time to earn the PPL through multi-instrument CPL, plus whatever instructor ratings you desire. Total cost in the US, somewhere between $ 50k and $ 80k.