More running

After not running from my accident in 1993 until early 2006, and then being unable to run once again due to foot pain in late December 2006, all of January through March, and most of April, I have been able to settle back into a routine of doing 4 miles a day (at roughly a 12 minute pace), and it's getting more comfortable day by day. This is an achievement about which I feel pretty good. But I hope I am not done yet. Several years ago, a good friend recommended the books of Clive Cussler to me, and I've come to enjoy them greatly. One main character is Admiral James Sandecker, a feisty septuagenarian who keeps fit by running 10K (6.2 miles) per day. I feel that if he can do it at his age, then I should be able to, also, so I've made that my goal. (Never mind that in the books, it's fiction.) I've jokingly told my daughter that I'll probably only run until I'm 90, and then cut back to walking. But how joking IS this?