Age isn't that big a factor, once your beyond the lower ranks and been in for a few years, age is determined by rank. It takes a few years at least, longer for younger men, to become a real soldier, but once you are, your rank is your age.

As for advice, I'm happy to answer specific questions, but I won't give generalized advice, feel free to NB me with anything. On that note, no, don't go into HumInt, actually I'd avoid any field that isn't combat arms, rank comes faster that way, much faster. Tanker, Infantry, Artillery, Combat Engineer - pick one of those, trust me on that if nothing else. Then get yourself deployed ASAP.

In some ways, that is really bad advice, because it will mess you up bad, but it will fill that hole, the others never really will, you can change MOS later. And join ASAP too, if you're biking twenty miles on a single workout you are more than ready, ask the recruiter for a list of combat arms slots available in the next month, pick the first, leave, do BCT, forget most of it, and move on.

Army Motto: FIDO - F it and drive on.

There's a lot of other things I could say, but that's all that matters right now. If you haven't done much traveling abroad ask for an OCONUS assignment in your contract, join combat arms, other than that, welcome brother, joining up is the best/stupidest thing you've ever done. But you won't regret it.