Here I am a 50 year old male, been running consistently for recreation and fitness since forever, 8 months ago started running in formal events (New York Road Runners) and found that I loved it so much I just had to get serious. Finished a couple 1/2 marathons with no serious difficulty, first at a 9:00/mile pace in January, then in May at 8:25/mile. A couple weeks ago I succumbed to the temptation to sign up for the Philadelphia Marathon on 23-Nov-2008.
I have been training sort of informally, 30+ miles per week, one 12 to 14 mile run per week and climbing, but I realize I am behind schedule on adopting a real program. So, a little Internet research and I find plenty of free generic programs (intermediate, advanced, etc) and a site -- runningplanet.com -- that offers non-free, specific goal-time--targeted programs. The latter is tempting me, and in any case I need to establish a time goal. By the "best 1/2 marathon time times two plus 10 minute" formula, I would shoot for 3:44. I think because of my age and inexperience in serious distance, I should be more conservative. The question I am debating is, shoot for 3:50 or 4:00?
PS To those who crawl around runners' forums all over the web: forgive the cross-post.
Interesting, the calculator you suggested tells me I should go for a 3:56:15 marathon -- roughly half way between 3:50 and 4:00. I guess I am in the ballpark.
One thing that as a newbie I find mystifying is the idea that I have heard: that you should practice at 80% of the pace you intend to maintain on race day. What sense does that make? Why not practice doing what you actually plan to do?
You can do both - running at 80% of your target pace allows you to run a long distance - 20+ miles when you've built up to it, while still being able to recover in a reasonable time. This can build up your endurance. You can also run shorter distances at your target marathon pace to practice that specific pace. Doing every long run at marathon pace would probably wear you out to the point where you couldn't get other quality runs in during the week.