I hit 50 mpw twice leading up to my 15th birthday.
I hadn't been super good as a freshman, probably running 25-35 mpw. I ran 5:42 for 1600 and 11:57 for 3200. There was a local 10k about 5 weeks after my track season ended that season and I wanted to do it. I also did anothe 10k as a tune up 2 weeks prior to the one I was aiming at.
I jumped my mileage up on my own for those 5 weeks and ended up going 39:45. The "tune up" race was 41 low (don't remember the exact time).
So, after a year of training at lower mileages, a jump in mileage worked for me. I don't know if I'd recommend doing it that way to anyone though. It's not how I coach my kids these days. As a poster above said, focus on strength, speed, general athleticism for the first year to 18 months then start ramping up mileage.
For me, I'm convinced that I didn't run well at the high school distances (as a freshman) because I didn't do enough stuff to be strong, fast and explosive. Most of my hard efforts were on the roads over 5-7 mile courses, so I was ready to jump in a 10k fairly soon after HS ended. However, we never worked on strength, speed, quickness in a way that I do with my athletes now. My best 400 that year was a 74.