This happens because the temperature at which oxygen changes from a gas to a liquid is about 13 degrees Celsius above that of nitrogen. The oxygen can be seen dripping from the can just as on a humid day you can see drops of water condense and drip from a can you take from the refrigerator.
Though you technically can join the military up to age 42, if you're 35 or over you'll need an age waiver if you've never been in the military before.
You also have to complete it, learning self-discipline and inner self-control. I think age 17 is too early for one to decide to join the military. A 17- or 18-year-old is not concerned with fighting for the country; teens are more into having fun and enjoying life while they can.