'Kay. The question. Googled and Wikipedia'd, but still clueless.
I'm looking for info on how old, on average, members of the army/marines at different ranks are, or how long it typically takes to reach certain ranks. Info on both enlisted and officers would be handy.
The main character I need to find this out for is a young, up and coming captain, who signed up as soon as he could. The world the story's set in is purely fictional, so there's a bit of swing room on the times/ages compared to real life.
Thanks for any help!