It is definitely possible, at 17 I was small for my age, skinny and physically immature, I ran but with no specific targets and probably around 40 miles per week. I ran 36.40 for 10k and then with harder training for a 3 month spell 35.20.
Fast forward to being 19, I had grown about 6 inches and weighed about 20lbs more, I still wasn't running great but I was training with a group and probably running 50 miles per week regularly but my lifestyle was rubbish, lots of drinking, late nights, skipped training. I didn't get involved with uni running teams and trained alone, I got down to 33.20.
The following year I was a bit more disciplined, maybe 60-70 miles per week with the odd double and a track session each week, improved to 32.28. around 4 months later I improved again to 31.23.
I then finished uni, relocated to a major city and got involved with some good training groups, started running to and from work and doing a long run. My lifestyle, diet was poor, too many late nights and regular drinking but was running consistently around 31 flat.
Age 24 I decided to run a track season and went from running 15.50's to 15.15 then 14.52 in my first track season at age 23, I was now running 70-80 per week with a long run of maybe 75-80 mins and one session and one tempo per week. Then had a winter of consistent training and some xc.
Age 25 I improved to 14.28 for 5k and was running 80-90 per week with 2 track sessions and maybe 3-4 double days where I would do a morning run of 4-5 miles.
Age 26 no improvement, suffered from Epstein Barr and took 8 months off running and had a very long frustrating return.
Age 27 probably consistently around 85+ miles per week, started adding long repetition sessions of things like 3 x 2 miles, 4 x 1.5 miles etc... and my usual track session of for example 10 x 1k. I only ran 14.40 this season with no improvement on pbs.
Age 28 I ran 14.40 in my first race of the season, then jumped to 14.10 and ran a 29.52 10k within a few weeks, followed that up with a 29.58, and a 14.11.
Age 29 I ran 14.14 in my first track race of the season and then got ill for much of the summer but ran 29.40 at the end of the season and then went on to run a 65.10 half marathon. By this point I was up around 100mpw week in week out and was running 2hrs + every sunday. Sessions would be something like 5 x mile at 10k pace or 8 x 1k at 5k pace etc...
the big thing for me was consistent miles, the introduction of long reps which teach efficiency, concentration and build strength and just waiting until you are physically mature and strong, you have to want it badly too.