Minimum running background for a sub 2:20 marathon.

1. 100 miles per week consistently over 6 months

2. Your week must include at least 1 long run 20-23 miles

3. "Specific period" 2-3 months in order to teach your body to be able run at 05:18min/mile pace (tempo, intervals, special blocks "quantity to quality", etc but no more than 5K pace speed)

4. Good luck.

had talent to run for a not awful D1 program

be able to sustain high mileage training blocks for a few years. id guess 80+ for 3-5 years with peaks at 100-110

now if you have more talent like a top 3 or 5 runner on a solid D1 program then you can get there in 1-2 years. if you are slower than the talent I had you may be able to do it but if you cant in 7 years of training then its unlikely you ever will

No background required. If a 2:03 marathoner started training at 20 years old, he could run 2:20 within 6 months.