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.
Across the United States Armed Forces, the maximum age for enlistment for someone who has never served in the military before depends on the branch. For the Army, the maximum age is 35. For the Navy, age waivers start at 34-years-old. For the Air Force, the maximum age allowed to join is 39-years-old. The Marines have the lowest maximum age for regular military service at 28-years-old.