Mar. 2013 (age 12 yrs, 2 mo.): 62 mph
April 2014 (age 13 yrs, 3 mo.): 70 mph
June 2015 (age 14 yrs, 5 mo): 75.1 mph
Looking good. The radar gun is a tool like any other. It measures something. IN this case progress. This is very nice progress. There are lots of places where a freshman throwing 75 with decent stuff and good movement is a starting varsity pitcher.
Thanks roothog, much appreciated. The high school that 2019Son will be attending is in the highest classification (Division 1) and the largest region (Southern Section) in California, and in one of the most competitive leagues, so there is no thought of varsity next year. 2019Son is aiming for JV, and hopefully he continues to make progress -- and puts on a little weight! (130-something pounds is not going to cut it! 
)
The pitching facility that he went to for the first time had the following chart on the wall for max velocity and max throwing distance, which I thought was interesting. It isn't so much "you will follow this path" but rather "given your goals, how do you stand right now? And do you need to pick up the pace?"
It's crazy how two similar players can have such different experiences based on where they live. My rising freshman who's at the same velocity as yours will be going to the smallest classification school in a bad district for baseball. His high school coach is drooling over him. Already asked me if I think he can handle the pressure of being the top pitcher as a freshman. Move your kid here and our team will be loaded hahaha.
I also found that chart interesting my son was on the bottom at 12, next level up at 13, and second level down at 14. Hope that trend continues to the top level at 15 lol.