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.
Traditionally, most people join the U.S. military in their late teens or early to mid-twenties. In 2011 the average enlistment age for people joining the Army was 21.3 years. Each of the four military service branches and the Coast Guard also have their own maximum age standards for enlistment or officer commissioning.