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.
(down time for training was short) Army Rangers well they do not spend 20-25 years in the Rangers. Its is a short tour but a hell off a grind to make it but its back to regular army afterwards. They are quite a fit group. Marine force recon, they are good but they are not Seals.