I ran my first 2:15 at age 32 but I think I had been in that shape years before at about age 24 prior to a sabbatical from running because I debuted a 2:17 marathon that year. My closing miles were pretty ridiculous that day - suggesting I had more in me had I had a knew exactly what I was doing.
So to answer your question: 4-5 years was all it took for me to enter the track&field news lists on that mileage.
My 10k was pretty weak: Close to 31 minutes when I began that mileage. I ran nearly under 30:00 a year later and then I took it to the marathon. Looking back, I should've explored my speed at mid-distances longer before moving up.
I'm pretty sure I had 2:12 potential in there on a perfect day. I ended up running 4:13 mile at age 34, probably because I had gotten so strong that even applying even a few 400's 200's and 100's was all it took. I couldn't run 4:25 in college before all that mileage. Seemed like any speed I applied to training, I could hold that pace for far longer periods of time on high mileage. I've never explored scientifically why that is.