I think there's about one 12yo prospect a year, maybe less in the country and a lot can still change in a couple years.
My opinions on this are strong but to be honest I'm not certain a July birthday is a good reason for holding a player back. That's on the margin of doing it to get an advantage rather than doing it to not be at a disadvantage. I wouldn't get angry over someone doing it, but I wouldn't recommend it either. Like everything else it depends on the individual and their family. There is no one right way of doing it.
Let's take a scholarship out of the equation. Almost every one of us has spent far more on baseball than we could ever recoup through a scholarship. We do it to see our son's get the most joy and fulfillment possible from the game. There really isn't any other valid reason for what we do although I'll admit most of us get a lot of satisfaction from seeing our son's continue to play baseball for as long as possible.