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.
Statistically, this past decade a majority of recruits fail to meet the height/weight standards of the military as the number one reason why people cannot immediately sign up for service. Here is a look at some of the basic qualifications to enlist in the military. Age Across the armed forces, the minimum age allowed for enlistment is 17 (with parental consent) and 18 (without parental consent).