Too late for ROTC
As a Senior, you're too late for ROTC, but you can consider Officer Training School, or OTS. My understanding is that OTS slots are very limited right now (easiest to gin-up or down as need dictates, while ROTC/Academy has more lead-time). Pilot slots in OTS are even tighter, although I have a student right now who is an OTS guy.
That would be too late for ROTC in any branch of service. But all the services have an OTC or OCS, for guys who already have a college degree.
I would not discount the Guard or Reserves, although again, hiring is down right now. The Air Force invested in junk bonds and lost their retirement portfolio. Kidding aside, money is tight in the military.
USAF and Army will direct-hire into the Guard or Reserves, but the Navy (to my knowledge) only hires prior-service. The Marines--same deal.
Of course, there is no "Navy Guard" or "Marine Guard" (the Marine guard is the guy with the rifle and bayonet).
Good luck.