"School age" could be defined in the order itself, or there could be something in the context of the order that sheds light on what the term means. Absent any such language or context it would normally suggest a child whose age places him or her under a state's compulsory attendance laws. See Texas Education Code, Sec. 25.085. That appears to be the general conception that Texas courts use when they address "school age" children in custody opinions.

How a court might interpret the language could also turn on the facts. If "this program" is an hour or two a week, then a court is highly unlikely to view your son's participation as indicating that he is "school age". If he's enrolled in the program for a full school day, every day of the standard school year, the court might take a different view.