I'd walked over 1000 miles of the AT before I turned 17. I did a 650 mile/2 mo's walk on it in 1977 with a friend on my summer HS break. I turned 16 on GA/NC border on the 21st of June that year. Tough summer as there was a heat wave and drought.
It's gotten easier due to lighter gear, the relocation of the trail (thanks to Jimmy Carter), and more re-supply points than when I was on it - we were typically 12-14 days between re-supply.
I'm still an active backpacker, and would have no problem doing it at my age (60 in June). PM me if you need any specifics.
But what I can say is, "there is no try, only do." Either you know you can do it, or you shouldn't bother. First, do a 2 week backpack and see how that goes. If you've never done more than a week's backpack you're out of your depth.
