I remember running 11.9 in the 100m and 2:11 in the 800m around 16 years old. I think 1500m was around 5 minutes and 5km was around 18-something. I got more involved in other sports from then until University.
This was in Ireland so smaller pool and I won a few meets at 800m and 1500m at that pace, even though not actually fast even nationally. Came 5th out of 8 in a 3000m steeplechase provincially once.
Had not the foggiest idea how to train and fitness was just from playing a range of sports. Coaches were generally just teachers who liked sports very much but rarely deep history in it. I probably couldn't even have told you what was a good time for anything over 200m. I enjoyed it though, and think there's plenty left on the table for time improvements in late 20s and 30s though I mainly run road races >5km and never track meets now.