Page 218 from Better Training for mid distance runners:
Generalized 12 day training block (Just the first 7 days):
1. 3x2k
2. Overdistance fartlek
3. 8x800m
4. Distance Running on Roads
5. 30x200m
6. Fartlek
7. Time trial
Having read all of the above suggested materials, there aren't actually a lot of good examples of Seb's training as a senior athlete. So this recommendation would probably be pretty good estimate seeing as his coach/dad set it out.
Lets assume 2miles WU & WD for each, that's 4x7=28miles.
Assuming his distance runs and fartleks are about 10miles, that's about 3x10=30miles.
Assume 2:1 rest ratio for the 2k intervals as suggested and you could cover 800m between the 2k's, so day has 1600m recvery, 2:1 rest ratio for the 8's gives you about 400m, so another 7x400m=2800m. Jog 200m between the 200m reps and you get 29x200m=5800m giving a total of 10200m or 6.4 miles.
Now for the actual workouts: 6km + 6.4km + 6km =18.4 km or another 11.5 miles.
For the time trial lets assume just 1mile.
So without any doubles we get: 76.9 miles or call it 75 to err on the cautious side.
But as an 18 year old (page 220) Seb did doubles 6 of 7 days, so we could probably safely assume 5 as a senior and again we'll just go 5miles to be safe so: 5x5=25miles.
75+25=100miles, but I could be off by a couple of metres or so...