I have created a chart below based on my former students. I chose to use Age as a factor to separate physical development. I also chose stride length to reflect pitcher height and overall strength. Tall pitchers usually have longer arms that can create more leverage for the pitch. Pitchers with strong legs can also produce more push and create a longer stride. Height and strength are direct factors in pitching speed.
Use this chart as a guide and not as an absolute. If you are below the average for your age, work first on developing more leg drive. This can be done through technique and strength training. If you are way above the average for your age, please be aware you are at high risk for injuries. Following a strenuous arm care program and staying below your pitch count will reduce injury potential.