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.
From 1954 to the early 1970's, the Army's goal, though seldom achieved, was to have one Ranger qualified NCO per infantry platoon and one officer per company. In an effort to better achieve this goal, in 1954 the Army required all combat arms officers to become Ranger/ Airborne qualified.