Hello there! I found the answer to your age question, and there is a limit. The limit begins at 20 and ends at 40, but the limit can be waived on a "case-to-case basis (up to age 51)." You can view more on this website:
http://www.navy-la.com/nurse.html Also, after you get your BSN, you go to the OIS (Officer Indoctrination School) which is only for five weeks. I finished my freshman year at college and I'm a nursing major. After I graduate from college I'm going to go into the Navy. If you need more information I'll be glad to give it to you. Good luck!