Went into the Corps when I was 26. P.I. wasn't too bad... just a matter of mental toughness. Just remember: Roy Boehm went through UDT / BUD/S twice... once when he was a kid, then again when he was 40. Went for 0311... Mark 1 Mod 0 grunt. Some things got in the way. Oh, well...
If all you're looking for is trigger time, yeah, you'll get alot as an 03 in the Corps. You'll also recieve the finest marksmanship training in the history of the human race. 03 not a bad MOS... when you're not in the field or deployed, you're time's pretty much your own. At the time, you could sign out an M16 and some ammo and as long as it was clean and back in the Armory by 1730, life was good. You'll get to play with alot of other weapons as well.
That being said, the 03 billet isn't exactly great career training. Unless you stay in, the skills aren't that marketable. You can also go armorer, MP, Range Officer, or get to the point where you can qualify as a Primary Marksmanship Instructor... transferable skills. That's probably where the other services have it over the 03 / Corps.... alot more skills that'll be useful once you get out.
My advice FWIW: if you're looking ahead for career training, the other services have more billets that cover more areas. If you just want to play with guns AND join the Corps, go reserve. If you hate the life, you just have to suck it up for a couple weeks a year and one weekend a month... unless your unit deploys (then " you numbah one f#$ky f#$ky"). If you love it, you can go active and the world's your oyster.
Good luck with your decision.
Semper Fi!
S.