In 1905, Levene was appointed as head of the biochemical laboratory at the Rockefeller Institute of Medical Research. He spent the rest of his career at this institute, and it was there that he identified the components of DNA.
It also takes anywhere from 18 to 24 months to get promoted to O-2 following entry to the Army, so the effective minimum age to join the Rangers for officers is around 23 to 24 years old. Officers can then continue to apply until they are promoted to O-5.
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.