You might be interested in past posts on this topic:
How did the nobility manage to hold on to their privileges for so long, even though they didn't really do anything in return?
^(24 Oct 2013 | 3 comments)
^(/u/DonaldFDraper describes pre-Revolutionary and Napoleonic French officer demographics.)
How did a person become an officer in the British Navy around the era of the Napoleonic wars?
^(10 Feb 2015 | 13 comments)
^(/u/jschooltiger describes the requirements for becoming a midshipmen and being promoted upwards.)
In Britain during and before the Napoleonic Era, what was more expensive - an officer's or a midshipman's commission? Furthermore, how expensive would these be today in comparable finances, and what kind of families did these young men and boys come from? Were they always necessarily super rich?
^(22 Dec 2015 | 6 comments)
^(/u/thefourthmaninaboat describes the requirements for becoming an ensign.)