Actually there is a lot more to it. You can buy back your AD time and only AD time. Inactive time (AFTP/UTA) does not count. You have 3 years to buy it back from the time you start then you incur a penalty. As for retirement, you need to meet you minimum retirement age (MRA) which depends when you where born. I don’t have the book with me right now but I’d say most of us would fit in the 57 yr old range. So as an ART officer you have a mandatory retirement age of 55 yrs old, unless you get an extension. To add to that the way I understand it is that if you start to collect your retirement before 55, you get a 5% per year taken away from you from 57, so you would lose 10% if you start to collect at 55. So in this case you would need to have 2 yrs stored or get a side job to fill the time in between.
As for the tax free down range, you do lose that for your civilian pay, but not the mil. You have to convert to mil status to go down range and that is tax free. It’s the most confusing pay system you will ever know. ARTs spend 4-8 hrs a week figuring out what they did, documenting it and then justifying it to the command bean counters. I say make all ARTs AGRs and save us the BS of it all! Life would be much more enjoyable!