Few years ago, I witnessed a patron with an unusually large child in a stroller attempting entry , the CM asked ate age and the patron murmered an answer. The child was permitted free entry. The CM commented to fellow CM referencing child, " better than last one which was probably close to 8." I'm sure CM's have seen it all.
As a mother my impression, the child did appear school age.
My son was large for his age, and I even considered bringing his birth certificate when he was your son's age. We had no problem.
My oldest son was the opposite, small for his age and could have gotten by with free admission for awhile, I chose not to and was even told once or twice he was "good" and I gave his age and submitted his ticket.
I am sure there are people pushing the age/free admission. What example are they setting for ther children? Also those that have legitimate size dilemma.