Marathons for the Average Runner

Through personal experience I know that the average runner with average health and fitness(in the legs and joints- not systemic health) can start from minimal movement and run a marathon in 9-12 months.
Now you won't go to the Olympics but you can toe the starting line and finish with fun.
This allows for 2 months to get started and be able to run ( better run/walk) 2-4 miles. At this point the athlete is ready to slowly start adding miles and milestones to the training.
Now we add distance and time to the training. Build distance up to the 13-15 mile mark over he next 4 months.
During this phase the athlete can and should run some 5k and 10k races. This will serve several purposes. A) have fun with a group of runners B) Learn how to run in a crowd and settle down and relax durng a race C) Learn pacing D) meet people and make friends to run with.
From this point on alternating weeks you add 1-2 miles to the long run or add 20-30 minutes to the long run. Ultimately you will run 20-22 miles and be on your feet for 4- 4.5 hours.

The first marathon will be an accomplishment and challenge but you will cherish the experience and the fitness gained during it.