M.S.
If his bowel movements are very hard and he's not pooping every day then you need to step in. You don't want the pain of BMs to be so bad that he starts holding them in, then you're in trouble. The only thing you need to do is add a little (like a tablespoon) of Miralax (over the counter) to his water, juice, milk, whatever. It is totally tasteless and non habit forming and will help make his stools softer. If a tablespoon doesn't help use a little more. I'd say start with just one dose per day and see what happens the next day. It will take about that long to have any effect on his stool.