Earlier quoted context omitted.
The US military also skews young but leans more towards the republican party. https://news.gallup.com/poll/118684/military-veterans-ages-t...
Looks like there are 1.29 million in the US military (0.3% of US population), with an average age of 34.5. (All figures from top search result of Google.) 59% of millennials lean or identify as Democrat compared to 35% Republican https://www.people-press.org/2018/03/01/1-generations-party-...
I don't know a single person in the military today that is over 30, and I live right by Nellis(Not exactly hard data, of course). Most people go into the military right after high school. I'd be surprised if the average age is actually that high, especially considering you can't even join the military over certain ages - though that depends on the branch and other factors. IIRC you cannot join the marines if you are >30
I suspect you probably are specifically looking at officers, which is an entirely different story.
[0]https://www.ncsl.org/blog/2017/11/10/veterans-by-the-numbers...