The muscle memory that they develop from starting this early is invaluable. Kids these days don't watch football like I did or most likely you did growing up. When I was a kid and went to HS football games on Friday nights. You got a bunch of guys together and played FB against kids from the other town. Now you can't do that. IMO it makes kids less aggressive. So starting them a little earlier puts a little of that back into them.
My son watches way more football than I did growing up simply because it's always on TV during the season. He is in HS now so he is actually on the side lines but before that, he was at the HS games watching or out back playing football with the other kids.
That is great that your son enjoys it. My experience with kids is that the majority of them don't watch a lot of FB till they get to HS. Neither one of my sons really watches too much football. My oldest, who is a senior, will watch a husker game with me, but that is about it. My 5th grader gets board with it. He will watch for about a quarter and then wonders off to do something else. He loves playing football, but just doesn't watch it a lot.
I used to get kids in 9th grade that had absolutely no clue about the rules of FB or how the game went. I used to ask kids all the time if they ever watch FB and a lot of them said not really. The other end of the spectrum was the kids that watch a lot of NFL and think that HS football is going to be just like that. Thinking we were going to throw the ball 40x a game.