The point of civil disobedience is to get the law changed. By quietly lying about your age, you're doing the opposite, you're making it harder to get the law changed. Civil disobedience is about adding friction to the system as an incentive to change the law. By doing something nobody can notice you're adding grease.
It's not civil disobedience if nobody notices what you're doing. It's not civil disobedience if you aren't inconveniencing people in power.
By lying about your age, you're breaking the law purely for selfish benefit, which is not the lesson a parent wants to teach a child.
Sacrificing himself by following the law, and spreading the story widely as the author and his son have done will do much more to get the law changed.