I had several classmates who joined AROTC after freshman and even sophomore year and earned commissions; it's not too late if you want to go that route. One was dropped from AFROTC after fall semester sophomore year, joined Army, and got an active duty infantry (he'll go to Intelligence later) slot. OCS might be more difficult but it is possible. In my BOLC class, there were several LTs who commissioned through OCS (active duty contracts) without prior military service. However, most of them had grad degrees; including a couple of PhDs. Again, this is all from the Army side; you should make sure to gather facts from the other branches. If I were in your position, I'd give ROTC a try for the semester. The worst that can happen is you decide it's not the right fit and drop; without it being a dead end to commissioning. Take advantage of the summer and do some research. Bottom line, if you truly desire to commission, do you research and seriously consider taking any opportunity.