Everything you're asking has been answered numerous times on this forum, apc military, as well as on baseops. In fact, there's a large thread about 4 down in this forum on the age subject. It's well worth your time to put in the research.
You need to be in UPT by your 30th bday, and putting a history of asthma on a medical form may be a dealbreaker for you. You're late to the game, but it's not impossible. If you want it bad enough, you'll do the research and beat down every door, call every number, rush every unit, and figure out a way. I busted my ass for years to get a flying job in the Reserves, and it was well worth the effort.
Good luck. 'Merica.