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.
The earliest age at which individuals can enlist in any branch of the U.S. military is age 17, but at this age, they must have parental consent. However, the average age is higher given that some people enlist later. The maximum age for most branches is 35. On its recruiting website, the U.S. Army reported an average enlistment age of just under 21 in 2012. This was slightly lower than the average age from 2010 and 2011.