Dude, I think getting out at 18 years is absolute lunacy. Here are my thoughts on some reasons why:

1. Money. You make good money now. You will not when you get out. It will take me maybe 8 years to make in the airlines what I made when I got out of the AF at 12 years. My airline job pays roughly 45% of what I made active duty. I do the reserve gig on the side now and I'm still NOWHERE close to what I was making before and won't be for several years. It's tougher than it sounds to cut back on your lifestyle to the degree we need to. Are you ready for that? Really? If you make it til 20, you will be paid just to breathe every day for the rest of your life. I don't know what you'd make in retirement, but for argument, let's just say you'd make 20K/year in active duty retirement (low estimate, I suspect) and you'd retire active duty at age 42. You're giving up 360K in retirement money until age 60, when you could possibly pick up less in reserve retirement. If they offered you a 360K bonus (or whatever the real number is) to stay in for 2 years, would that help you stay? They are offering it...in the form of active duty retirement.

2. Health care. You never think twice about it on active duty because you don't pay a dime. We now get bills in the mail every time the kids go to the pediatrician. That sucks. If I lose my job, I lose my insurance. That worries me. If you retire from AD, you will always have health insurance no matter what. That's a BIG DEAL. My inlaws are retired and completely healthy. They pay something like $1800 a month for health insurance. Did I mention that they are completely healthy? Health care costs/insurance costs are only going uphill. While fees may rise for Tricare down the road, at least you know it's there for you and they can't take it away if you lose your job, get sick, etc.

3. Security. There is absolutely none on the outside. I have no idea if I will have a job this time next year. I will NOT have an active duty retirement to help out with the bills if I get furloughed. There is a lot of uncertainty in this industry and that will never change. Though active duty retirement obviously doesn't save you from furlough, it is a financial and health care safety net if things go south.

4. Commuting to an airline job sucks and sitting reserve at an airline job sucks. I do both and sounds like you would too, at least at first. I suggest you check out the search function of this thread and you can read a lot about that stuff. That obviously doesn't change based on whether you retire off AD or not, but chalk it up in the "grass ain't totally green" and "drudgery" categories.

5. The dudes who mentioned it are right. You can't just serve 2 years in the reserves and pick up a reserve retirement...it's 6 yrs min. Plus, it will take you a LONG TIME to earn enough points to cover those 2 years to pick up active duty retirement...unless you can pick up some orders and/or work every day off you have in the airlines plus taking some mil leave to work more. If you are going to work that much anyway, why not just stay active duty?

I hope I don't sound harsh...don't mean to be. I just got out in September, so believe me I know all the things going through your mind. But I'm now out here without the safety net of an active duty retirement, and it SUCKS. I don't even know you and I practically feel like begging you to stay those 2 more years. I think you'd be absolutely crazy to punch out now. I think you would look back on that decision as a terrible mistake.