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.
Requirements for Joining the U.S. Military. To join the enlisted ranks, in general you must: Be a U.S. citizen or Green Card holder Non-citizens must speak, read, and write English fluently. Non-citizens must currently live in the U.S. Be in good health. Be 17 to 40 years old (different branches have different age requirements).