I'm no fighter pilot, and I never flew in the Navy. But I've got a pretty good view oft he AF fighter life from the outside. The age thing is all about "becoming part of the culture".
It's much easier to inculcate a 23 year old into the fighter culture than some that are pushing 30. OptionsDollarAir alluded to this. Same reason the AF is a bit discriminatory toward FAIPs (e.g. SERGRADs) going to fighters... my opinion.
The pre-frontal cortex isn't fully formed until age 25ish. There is a big difference between someone who is 23-24, and 28-30... both in terms of where they are in their family life, spiritual life, financial situation, etc... And it's not always conducive to the AF culture of "the fighter squadron" and becoming an integral and trusted part of it. To be clear, It requires spending a lot of time focusing on becoming smarter and better. Worthy goals... but a potentially hard and conflicting lifestyle.
You've got to decide if you want to become a significant part of that culture, or just do a touch and go after trying it for 5 years, and then move on.
Age, from a physical standpoint, is s a non-event when it comes to flying fighters.
BTW, I know a guy that showed up at USAF pilot training in 2018, 1 month before he turned 40... as a 2Lt. Reservist.
Well. Maybe not time spent on becoming smarter and better, but being easier to condition to kill another human being.
I believe the instances of PTSD in Pred/Reaper crews is related. The AF as a whole doesn't condition their officers to be practitioners of violence the way other services do. For instance, in the Marine Corps one of the first things you learn is your 4 weapon's handling rules- then you put a BFA on and start aiming and pulling the trigger at other Marines in the field. Treat every weapon as if it were loaded, never point a weapon at anything you don't intend to shoot, keep your weapon on safe until you're ready to fire, keep your finger off the trigger until you intend to fire. Then we look down the sights of a real weapon, aim for a living person's head or chest and pull the trigger with blank ammo loaded.
The Marine Corps is also the youngest service. I believe that's by design on a certain level. It's much easier to condition an 18-22 year (who's brain hasn't fully developed yet) than it could be a 28 year old.
Yet if we look at how the USAF selects (or selected) RPA folks, it was folks who didn't do very well in pilot training. Perhaps they joined the AF to be a cargo type, perhaps they never wanted to kill, they wanted to fly. Now they're sent to a community that does (well, did... we're not nearly as busy as we had been in the past) a lot of killing, and a lot of hanging around and looking at the killing we did. We're putting people in positions without the proper conditioning.
So I see merritt in the "Fighter Pilot" thought process for the Air Force- I believe it's one of those few communities that have to condition someone to be ready to kill in the Air Force. I really don't think the officers and NCOs of the Air Force ever get conditioned to think about mortality in warfare- until they get to a few select communities. I think we need some of it in the RPA community (minus all of the stupid rules and words and elbow pointing). I can't speak to the Navy OCS process, but I know they have Marine DIs, and I imagine there is a level of "you'll drown at sea and get your entire crew killed if you suck". I could be wrong though.