I agree with the above. I am 59 and did a thru last year 2013. I saw many young uns on the trail early on with over use injuries, knees, ankle, blisters, and the like. Some of them got off the trail. I started slow in Georgia and took many zero days in the beginning. In Virginia I picked up the pace and was doing over 20 miles a day and got my first shin splints ever. Listen to your body the parts you think will give you trouble probably won't, and the parts you think won't give you trouble will. I finished strong doing high miles in very rugged terrain through NH and Maine.