I consider 9 and 10 to be the cut-off age for lessons. Of the kids that age, some are able to comprehend and perform what's taught to a reasonable degree while others are not quite ready. If your son is not to that point yet, save your money for another year or so.
As for the walks after two innings, it could be anything. Maybe he tires then. Maybe his mental state changes. (Does he worry about getting taken off the mound or out of the game at that point?) Tough to say for sure.