Sorry if this is long.
I am a 19 year old guy who started running freshman year of HS in XC, so I've been running for a little under 5 years. Didn't take running seriously at all that first year because I wasn't into the sport yet (my training was very sporadic and screwy and probably averaged around 10-15 miles/week throughout freshman year). Got down to a sub-20 5k by the end of XC and ran 5:10 mile in track. Made me think I could have decent potential at running if I started training correctly. Summer going into sophomore year is when I started training "seriously." Finished my HS XC career with a 16:30 5K, however that was on a flat, all pavement course, the rest of my performances were low-mid 17's. (put in 70-80mpw the summer prior). Senior year of track is when the frustration started. I had a goal of going 4:30/10:00 for the mile/2 mile. My PRs from the year before were 4:48/10:30. I thought this was doable based on the strength I developed in XC and thought the times would come down when I started doing more track-specific speed workouts.. Well, I did do speed and only ran 4:50/10:27 in track, so no PR in the mile and only a small improvement in the 2 mile. I was secretly glad when the season got cancelled because I was very frustrated about this. Spent March-August in a running funk, trying different types of running to try to get in better shape but it wasn't working. I wasn't going to run for a college team and my lack of improvement for track made me wonder how I would do at the longer distances. Felt like my body was finally responding to training in September and I started training for a marathon in October and peaked at 100mpw in the winter with plenty of solid workouts. Ran a 2:42 marathon in March (Was very windy on race day and I feel I peaked a little too early in my training cycle, so I think I was capable of 2:36-2:38 at one point). I finally felt satisfied with my running but now it has just gone back to what it used to be like, putting in the work and just not feeling like I'm getting any fitter. I seem to be stuck at around a 60 VDOT (4:55 mile, 17:00 5K, low 2:40 marathon) for the past few years. I want to get down to running a 4:30 mile and sub 16 5ks but it feels like that is just never going to come. Did I truly reach my peak. Does it really only take 5 years of running to do so, or can it take up to 10 years?