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.
Rangers in the US Army consist of the 75th Ranger Regiment's Special Troops Battalion and First, Second and Third battalions, and the US Army Ranger School's Fourth, Fifth and Sixth battalions of personnel undergoing individual Ranger training.