Ran my first marathon 2 years ago at age 51 and ran 3:49, died on the last 6 miles.
Also did my first marathon in 3:49 2.5 years ago but age 41 at the time. My best marathon so far was on the day that we should have beaten PSU. Finished 3:25 that day and then hours later watched the game in the hotel on my iPad. I'll be running my first 50K this coming August on a beautiful but very difficult course.