As usual, Garlic is quite correct.
I'll just encourage you to get in shape...
The hiking will be more enjoyable and you'll have less health problems in the long run!
One way to get in shape is to get in as many hikes and backpacks as you can between now and next March.
Not only will it help to get you in shape, but it is fun and will help you iron out the kinks in your gear kit and hiking style BEFORE you start on a 5-7 month hike.
If you are in shape, have your kit and style dialed-in and have some prior backpacking experience, I think you will find the typical rough shake down period that many AT hikers have will be a bit smoother. They'll be taking lots of zeroes in town...you'll be having fun in the woods!
Good luck..and have a blast!