To answer the original question, your premise is not too far off base. 24 is pretty close to the lower limit for a qualified Air Force fighter pilot that graduates college or the service academy and is commissioned at late 21/early 22 years old. Approximately 1.5+ years in flight training and an aircraft specific Replacement Training Unit (RTU) if that's what they are still called. That includes time to move between bases and get ancillary training like survival training. I would imagine the Navy adds a bit of time for carrier qualification, but would guess the time line isn't too far off. Astro might provide some better information on that.
If said pilot is fortunate, and goes to a front line or remote unit (like bases in Korea) he gets great training, and becomes truly mission ready pretty quickly. If he goes to a stateside unit that is on the bottom tier for funding and the unit is sitting on a lot of broken aircraft, it may take him a couple of years before he is really qualified.
I've flown with some great Major and Lt Col fighter pilots, which would put them in the 33-37 year old category. Some manage to maintain their skills after that, but it seems to be the exception rather than the rule. I've also seen a very few General officers that were excellent sticks, but if I were king, I would forbid every officer above the rank of Colonel to sit in a single seat fighter or in the front seat of a dual seat fighter. The reason for that is some of them start to lose judgement, nobody can tell them no, and they think the rules don't apply to them (effectively they don't). There have been some spectacular accidents with senior officers involved, yet somehow they never seem to be at fault.