WilliamC93:
This may sound a little harsh, but I want you and everyone else reading this to get this message loud and clear. Get to the MEDICAL recruiting station now, do not pass go, do not collect the $200.00, go directly to the recruiters now. Start the process NOW. Not in August, and certainly NOT in September. There are a whole lot of little things like personal statement and letters of recommendation that you need to get on top of a pile of papersork litterally a foot high that you need to review and sign not to mention the physical and any waivers (moral or physical) that may arise.
Can you apply to more than one Service? Yep. Should you? We can't tell you that. It seems that it SHOULD be a part of your motivation for wanting to serve your country and those who volunteer to defend it. My (name a friend or relative) served in the XYZ service until he could retire and said it was the best job in the world or I've wanted to be a part of the XYZ service since I was a little kid or some such.