Just one man's opinion: work hard enough in ROTC and you will get a pilot slot (pending medical stuff out of your control obviously). OTS is not a bad route, but it certainly takes more luck/timing and seems more volatile than ROTC. While in ROTC, I saw MAYBE two dudes in four years not get a pilot slot who probably should have, the rest who applied and didn't get one was of no shock to me. There is no guaranteed route without its own set of timing/luck hurdles. Based on your age you really have one (maybe two) shots at this. Personally if you have to throw all the chips on the table, I think ROTC probably offers you the best chance. The "worst case" if pilot doesn't work out, you serve your country for 4 years, probably still have a good time doing it and set yourself up well for a post-military career. If you really want to be a pilot, then I think that "4 year non-flying" thing is a risk worth taking.