The ASVAB is the Armed Services Vocational Aptitude Battery
It basically tests you in many different areas, mainly related to career work. To get into the military, you need at least a 32. You should be able to get much higher though. And the higher you get, the better opportunities you get. I got a 94 on my ASVAB and I had recruiters from all the branches calling me before I had even gotten my test results because I had listed Military as my occupation after high school.
The physicals tests aren't that hard. You should be able to pass them even now.
Also, some other requirements are that you must pass a full physical examination at MEPS. (Military Entrance Processing Site) [I think.]
And you must clear a background check, and there are many, MANY forms and paperwork you must sign.