Dave: I also used the Runners' World Smart Coach training plan. I think it's a good combination of long, easy and tempo runs. It was also easy to customize for the target distance and the number of weeks of training. Like yours, it built up the distances gradually and allowed for a decrease every four weeks.
Going easy for the first few miles allows a thorough warmup and makes the rest easier. The fact that you're not puffing as much during a run means that 1) you are getting fitter and 2) you're learning to pace yourself. I drink a fair amount of water with Gatorade G2 before I leave and I carry a water bottle fanny pack and Power Gels.
There's nothing wrong with starting running at age 50 or beyond. There's another thread on this forum called "Over 50, 5K and Beyond-What Are Your Challenges". No requirements for distance or speed, just be at least 50.
--Steve
Completed in 2012:
The Qualifier HM, Midland MI, May 2012, 2:58, 80+ degrees
Dam to Dam 20K, Des Moines, IA, June 2012, 2:17, PR for this race
Garry Bjorklund HM, Duluth, MN, June 2012, 2:20
Fox Valley HM, St. Charles, IL, 9/16/12, 2:23
Des Moines HM, 10/21/12, 2:19
Tentative plans for 2013:
Wisconsin (Half) Marathon, Kenosha, WI 5/4/2013 (registered)
Dam To Dam 20K, Des Moines, 6/2/2013 (registration opens March 20th)
Grandma's (Half) Marathon, Duluth, MN, 6/22/2013 (if I get picked again in the lottery)
Des Moines HM, 10/20/2013 (registered)