Well first off, you need to be sure what branch you would like to join. According to your list of questions...last week you asked a question if you were ready to join marine boot camp. Do your research and find out which branch is right for you. The army uses the Army Physical Fitness Test to determine if you are fit enough to serve. I've listed a link below to the standards you'll need to reach and hopefully that will give you some insight as to how ready you are according to your height and weight. Good Luck!
http://www.army.com/enlist/APFT.html