For AFROTC:
Yes. You are able to apply for the program as a sophomore. You will be what as know as a 250, and will be expected to cram about two years worth of ROTC work into one year.
You can apply for a scholarship halfway through the year. Just some advice though. If you do AFROTC just for the money, you'll most likely have a pretty miserable time if a scholarship is your only motivation. Scholarships are not guaranteed, and depending on how much money the Air Force has available, they may not give any out in time for you to get one. In fact many cadets go all four years and never earn a scholarship. Also, after sophomore year, your package is put before a national board to see if you will be retained in the program, and if you are cut you will lose your scholarship. The only bright side is that if being an Air Force officer is more important than the money, you have the same chance to earn a commission as an officer whether on scholarship or not.
That being said, if you do want to be more competitive for a scholarship, choosing a tech major (engineering, weather, computer science, etc.), kicking butt on the fitness test (high 90s), and having a good GPA and SAT/ACT score will all help, as the scholarships are merit, not need based. Like I said earlier though, there is no guarantee and either way AFROTC is a pretty major time commitment. You won't find out if you got a scholarship until halfway through the semester.
Also, not all scholarships are full tuition, especially if you are coming from out of state. Type, 1, the most difficult to get, is full tuition to any school in or out of state. Type 2 and Type 7 are full tuition to any in-state public university. If out of state, Type 2 covers up to $18,000 a year and Type 7 covers just the in state rate. with you paying the difference.
Not trying to scare you away, as a few of the freshmen at my detachment have earned Type 2s, 7s and even one or two type 1s this semester, but it's not something you can really count on, especially at Embry-Riddle, which is one of the largest and most competitive ROTC detachments in the nation.
