Saorry I missed this one earlier, guys. 
The Service hires from the military (Operations Shining Star), colleges (the co-op program), and general public. They focus on one of those 3 ar any given time, depending on the flavor of the the day.
Obviously, getting co-ops they can be as young as 21-22. More typically, our ages run from 25 or so up to 35.
Back when I was hired, my class had mostly guys with degrees and LE experience, both, and some also had military. A few of us were lacking one of the 3, but made up for it in other ways. I was 24 when I was hired. I had a classmate that was 23 and another that was 36. The ages really vary.
Take Tex's advice. Be in shape. Don't waste yours, mine, or the other fit coordinator's time. 
BTW, the last few guys I know to have gotten offers were in LE already... local PDs.
We bring evil things to evil people, kicking in a door near you!
."In theory, there is no difference between theory and practice. But,
in practice, there is."
- Jan L.A. van de Snepscheut
"The difference between 'involvement' and 'commitment' is like
an eggs-and-ham breakfast: the chicken was 'involved' - the pig
was'committed'."
-unknown
Working on a PhD in CQB one doorway at a time.
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