I am 18 years old and I discovered the existence of PE when I was around 15 years old but I didn’t have either the privacy to perform the exercises or a way to obtain a device.
I only started PE seriously as I turned 18, as I was allowed more privacy and I got access to my bank account so I could purchase any device I pleased.
I kinda feel lucky for having discovered and started this early on, as I have obtained fast gains, probably due to the higher amount of testosterone.
I have performed PE responsibly without causing damage but I think many people my age would easily become impatient and risk their health to obtain faster results.
So I think that before telling any family member about PE you should assess their emotional maturity: think about how will he act if he doesn’t get good gains (think about how well does he handle losing, if he responds excessively it is a red flag), and if he is able to control himself properly (he may become obsessed if he is unable to control his feelings, what would end with him overtraining and probably hurting himself).
You should also be very careful about how to approach this subject. I would feel very awkward and embarrassed if my father talked about PE casually.
So I think you should only mention it if he asks you any question regarding PE or if you have a conversation about similar subjects (breast augmentations, surgeries or even bodybuilding) and you’re able to steer it into PE smoothly.
So in conclusion I think that not every teen would benefit from knowing PE (some of them may be too immature and prone to injuring themselves) but it can be extremely helpful for those who are having negative experiences in school for having a smaller than average instrument, as penis size is probably the most important thing for teens. At least here in Spain people with small penises are common joke targets and gossip about size is rampant. Personally, I had negative experiences in Gym class since I was an extreme grower to the point of avoiding showering after class, and completely avoided dating due to feeling insecure and inferior. So I would say that PE largely benefited me since I have lost almost all of these insecurities. So please if you can and he is mature enough avoid him the torment of feeling insecure and inadequate during the years where he could be enjoying his sexual life the most.