how long did it take you to go from sub 17 to sub 16?

I know a couple people in high school that went from low 16s to sub 15 in a couple weeks. (they had junior PR's in the 16's, but broke 15 their senior year)

so the question is kind of irrelevant there are different seasons and a lot of the improvement comes with the work you put in between the seasons when you might not race at all.

I only ran 30-35 mpw on average in the summer of HS, with a few at 40 and a few at 25, began senior year with a 36:30 10k XC time trial (admittedly on a hilly course, solo, and on a hot day), ran a 17:05 for the first meet (small league meet) we had and ran 15:40 a month later in good conditions. Ended up running under 9:10 that year in outdoor so I’d be shocked if I couldn’t have run under 15:00.

I never ran much mileage during track (no more than 40) but did it all under 6:30.

Mostly, the rate of improvement is more a reflection of raw talent than training. When you hear of HS boys who run 17:xx their first race and then 16:xx shortly after and by the next season they are at low 15s it's because they are extremely talented. Most kids need to train consistently for years to get there. Sub 15s are very talented kids and most will never get there despite any training they do.

There are some people that broke 17 but never made it to 16. The possible range is somewhere between a few weeks and infinity.

Totally agree -- talent/genetics play a role here. I'm under the belief that if someone is young, can stay healthy, & runs a good # of miles then they can break 17:00. Some would still struggle to break 16:00 or never run much faster than that. Others break 16 pretty quickly into HS XC on very little lifetime mileage. Those are the people who have a chance to go under 15 & 14.

With pretty good genetics and consistency, you might see a progression similar to mine

Freshman HS: 17:4X (XC)

Sophomore HS: 16:3X (XC)

Junior HS: 16:0X (XC)

Senior HS: 15:4X (XC)

Freshman College: 14:5X (Track)

Senior College: 14:0X (Track)

Each minute goal would be progressively harder - unless you trained significantly more or something. If you aren't breaking 17 in hs, sub 14 is unlikely but you might see sub 15 in college. A lot of guys don't even get down from high 15s to low 14s in college.

I broke 17 and 16 for the first times in my junior year. Not sure exactly when I ran sub-17 the first time, but it was late-September invite. Broke 16 at states in November.

Didn't break 15 until college, but I ran sub-14 sophomore year college (Age 19).

Never broke 17 in HS, then I had a breakthrough race soph year where I split ~16:30 during an 8k. I was probably in 16 flat or faster shape from that point forward, but I mostly only ran the 1500/800 during track season. Finally ran 15:35 on the track eight years later.

I'm not obese or lazy so I never ran above 16 min...