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.
Before Serving in the Army Reserve. Before Serving in the Army Reserve Before Serving in the Army Reserve To enlist in the U.S. Army Reserve, you must be between 18 and 35 years old (17 with parental consent). You cannot be older than 35 years. You must be a U.S. citizen or resident alien.