Former high school teacher; enlisted last summer at age 34. I felt the same way as you seem to - I wanted to do my part in the War on Terror rather than sitting around someday wondering why I let my country down when I was fully capable of serving. I enlisted in Armor (tanks) but was assigned to an Infantry unit in Fort Lewis, WA. We are getting ready deploy to Iraq soon although I can't give an exact date. It seems like most of Lewis is deploying right now - 3rd Brigade to Iraq, 4th Brigade to Iraq, 5th Brigade to Afghanistan, 17th Fires Brigade to Iraq, I Corps to Iraq, ... if you enlist in any combat arms branch to fight rather than shuffle papers behind a desk you WILL deploy. Nearly my entire company is looking forward to the coming year in the Sandbox, with a few exceptions who just returned from a deployment last year, a deployment that saw them lose six men.
Basic is not as hard as some will have you believe (Army perspective; I've heard Marine Basic is worse). Certainly try to be an officer as life will suck in the Army at your age if you are not an officer and not married. I was too old to go to OCS so I enlisted and entered as an E-4. Problem is I am not married so I was assigned to live in a barracks with mostly 18- to 24-year-olds who often times do not act much more mature than junior high students.
When you are in the field training, life is better than anything you could ever do in the civilian world. If you like living in the outdoors, eating shitty food, working hard all day (and sometimes all night), learning to function on little sleep, etc., then you will love an infantry unit. The comraderie developed during the challenging times is unmatched and you will only get closer once you arrive in the Middle East.
One thing to consider in your unique situation is what to do with all of your belongings. Unlike most new recruits, I had a large apartment full of belongings. I ended up selling all my furniture along with some other things once I found out I would be in a barracks rather than an apartment. Most of my things are in a 4x8 storage facility off post right now since I can't fit them in my room. After I get promoted I will have the option of getting an apartment and actually having all my belongings on hand.
If you feel the "need" to serve, then do it. If you don't you will regret it later. Even if you only do one 3-year tour, you'll end up deploying and doing your part. My company commander is preparing for his 4th deployment in 8 years in the military. If more young people would do their part and sacrifice just a couple years of their life for their country, we wouldn't have so many soldiers doing so many deployments. It's tough on families when Daddy is gone for a year, home for a year, gone for a year, ...
Nobody could say it better than General Patton on the eve of the Normandy Invasion:
"There is one great thing that you men will all be able to say after this war is over and you are home once again. You may be thankful that twenty years from now when you are sitting by the fireplace with your grandson on your knee and he asks you what you did in the great World War II, you WON'T have to cough, shift him to the other knee and say, "Well, your Granddaddy shoveled shit in Louisiana." No, Sir, you can look him straight in the eye and say, "Son, your Granddaddy rode with the Great Third Army and a Son-of-a-Goddamned-Bitch named Georgie Patton!"