Actually, you can prob walk on a little late, depending on where you go. Contact your det now, as most schools have a New Cadet orinetation the first week before classes start. You may be attending a crosstown school, which means you will be travelling to your host AFROTC school for classes. As a rising sophomore, you have two options. One is to go in as a 250, it's a dual program, where you do the first two years of rotc in one. The second option, is to go into rotc as a freshman in the program, and then extend your degree out a year. There are pros and cons to both options. You just have to figure out whats best for you. right now, you need to contact your det, if your school is the host school, go talk to someone there, and sign up for classes! Be prepared to have a challenging and rewarding year!