How did Lt. Greenhill become a Lieutenant?
The Searchers (1956) was filmed from July to Auguust 1955. https://www.imdb.com/title/tt0049730/locations?ref_=ttrel_sa_4
Parick Wayne was born July 15, 1939. https://www.imdb.com/name/nm0915618/?ref_=tt_cl_t_17
Thus he was aged either almost 16 or just barely 16 when his scenes as Lt. Greenhill were filmed.
And he certainly doesn't look much like an adult officer. At that time the main source for new officers in the US Army was West Point. And at that time the admission age for West Point was already set at 17 to 22, and it was already a four year period of instruction, so officers would graduate and be commissoned between the ages of 21 and 26, most at age 22.
So as a general rule even the greenest lieuteanants like Greenhill should have been about 22. I think that it might somehow be connected with the Civil War of 1861-1865. Unfortunately, The Searchers (1956) begins 3 years after the war,probably in 1868, and ends after a 5 year search, which is when Lt. Greenhill appears. So Greenhill is a very young looking officer in about 1873, 8 years after the war ended.
So if Greenhill in 1873 was the age of Patrick Wayne, he would have been born about 1857.
If greenhill became a lieutenant in the United States Volunteers during the war, and then managed to get a commission in the United States Army after the war onthe basis o fhis war service, he would have been only about 8 when the war ended. Taht would be old enough to be one of theyungest few drummer boys in the Civil War, but guite a few years lyounger thantheyoungest officer there.
Maybe Colonel Greenhill, in command of Lt. greenhill's unit in 1873, was in command of a unit during the Civil War and had his little son with him asa bugler or drummer boy. And maybe Colonel Greenhill was able to get his son into West Point about 1869 because of his son's service and possible heroism during the war.
Posssibly Colonel Greenhill ied about his son's age when appyling to West Point aobut 1868-69.
Possibly Colonel Greenhill had an older son who was a very young teenage officer during the war. Maybe theolder son died sometime after the war, but the c?olonel had his younger son impersonate the older son to get into West Point about 1869, or to get a direct appointment from civilian life around 1873.
I note tha t regula army officers wouldn't approve of their relatives serving as enlisted men (or boys as the case my have been). But officers in the United States Volunteers during the Civil War sometmes did have their sons and relatives enlisted in their units. So if Greenhill was a former Volunteer officer appointed to the regular army in 1866, he might have a volunteer officer's williness to have an enlisted son or other relative. And it was possible after the Civil War for a small fraction of enlisted soldiers to become commissione dofficers. So possibly Colonel Greenhill had his young bugler son apply for such a commmisison and had the other officers in the unit support the application and exaggerate the son's age.
As you see I am coming up with several rather improbable ideas to explain how someone as young as Patrick Wayne's Lt. Greenhill could be commissioned in the US Army.
Possibly Lt. Greenhill actually was 22 and merly looked many years younger than his true age.
I note that there is a similar problem in another John Wayne film directed by John Ford, Rio Grande (1950) where Jeff Yorke has already entered West Point and been expelled, despite being portrayed by 15-year-old Claude Jarmen Jr., and the minimum age to ender West Point being 17.
https://moviechat.org/tt0042895/Rio-Grande/62ce26d1921c7c55deec7a87/When-was-Jeff-born
In my post about that I wondered whether Rio Grande (1950) could happen in an alternate universe where there was a much younger minimum age at West Point - like most films set in historical eras it has to happen in an alternate universe to real history anyway.