I am way old school. Back then we talked about "respecting the distance." Meaning you didn't want to try a marathon until you were seasoned and ready. No sense in running a 3:00 or 3:08 just to finish, you wanted to be ready to run close to your ability.
I had one and half DNSs at 22 and 23 before running my first at age 25. I overtrained for DNS1 (Paavo Nurmi 1980), going along with my more experience teammate who swore that back to back 20 milers on the same weekend was a great way to train for a marathon. That resulted in my first experience with ITBS.
DNS2 was kind of a half hearted effort--I was going to jump into Grandma's (possibly as a bandit, because it was June already and I think the entry quota had been filled ) because I was living in the neighborhood. Had been running 60s/week through the spring with regular long runs of 12 to 15 miles, and bumped up the long runs to 19 or so. Stress fracture after just a couple of weeks.
At 25 I had matured a lot as a runner and got it right. Did weekly 17 to 20 milers (often ~50% easy, ~50% marathon pace) for about 2 months with no hitches along the way. Knew I was ready race after PRing by a minute for 10K, just two weeks out. Yes, ran for time, and completed the marathon at sub 6 pace at altitude.
