Over 50. I have followed some local HS distance runners just because I got to know them when they came to do some workouts with my training group. This was a few years back before everyone had instagram, etc. So, no one had any social media to follow.
On the national scene, I have little interest in HS distance runners except for the occasional stand out that gets to run a pro meet or breaks a record. And that is it. Kids develop at very different rates and being a top HS runner does not always translate into college and pro success. Boys who develop very early can be standouts in 9th grade and then washed up by 11th when all the other kids catch up.
Beyond the creepiness of old guys following HS sports is the really bad trend of forcing HS kids into high pressure national competition. When I was in HS in the 80s, there was a girl at my school who won state and went on to be an NCAA finalist. She had lots of trophies and a nice glossy photo of NCAA finals. And that was it. When she PR-ed, she did not get accused of doping. When she got hurt before a big meet, she did not get harangued for ducking the competition. Outside the very small community of top distance runners, no one even knew who she was.