Carbs, fats and proteins can all be used to produce glucose. Your body thrives on glucose, which is the sugar it uses to synthesize energy. Carbohydrates supply glucose and other sugars that are converted into glucose. But it's such a vital source of energy that the body has a back-up system called gluconeogenesis.
On its website, the U.S. Navy doesn't provide information about the average enlistment age. It notes that you can join from ages 17 through 34. The U.S. Air Force Personnel Center website doesn't provide an enlistment age average, but it does note that age 29 is the average age of its enlisted force, as of 2013.
Army - 35 (must ship to basic training prior to 35th birthday. The Army experimented with raising the age limit to age 42 for a brief period of time, but effective April 1st, 2011, the Army has reverted to the lower age limit. Air Force - 39. Navy - 34.