I posted a similar question recently, because I was not sure if I was psyching myself up or psyching myself out. I start hiking THREE MONTHS FROM TODAY.
This will be my first extended thru-hike, although I spent three weeks on the John Muir Trail this summer.
I encourage you to train, both physically and mentally. Read up (skip Bill Bryson's book... he is very negative. Check out "AWOL on the Appalachian Trail" (a forty-something husband/father) and "Becoming Odyssa" (a young woman just out of college) so you get a sense of the experiences of other first-time hikers. And be prepared physically so you know what your body can handle. Make sure you have decent gear and that your shoes/boots are broken in.
But being nervous about a six-month hike is natural. I look forward to meeting you along the AT.
Ross / DirtyGirl