Marathons are more than just about running. The training regimen taught me more about myself, then how fast or far i could run. Being in college at the time, the early morning training sessions lasting between 1 -4 hours, monday through saturday, and strict daily bedtime dictated that every minute of the waking day had to be spent wisely.
Its a pain to start the work, but its highly addictive once the schedule is in motion! I highly recommend doing this at any age.