I think that will come out in the training book Hilly as it will by its nature be based on my experience.
In a nutshell, I was pretty good from an early age. When I was 12 I ran 800 in about 2.10 to finish 2nd in the British Forces Schools Germany champs and sub 60 for 400 (I also finished 3rd against the local army teams in an orienteering race, which must have looked odd cos at 12 I was a tiny kid against fully grown squadies).
At 13, having moved to Folkestone from our miltary home in Germany and joined a club I finished 144th in the English Schools XC, progress was gradual from then and I won the English schools 5000m in my last year after being around 6th or 7th consistently over 1500m. 3 yrs at teacher training college didn't help progress much, but I ran with Brighton & Hove and trained with Steve Ovett while I was there. It wasn't until I moved to Canterbeury with my first teaching job that I made any progress - and it was basically that the runners at the club there (Invicta) were all preparing to run a marathon at Essone near Paris - I did all the heavy mileage with them and decided at the last minute to run it - I did 2.21 and the rest, as they say, is history.