Our friend explained that rules are necessary when children are young. Black and white is what they need. But, as they mature the rules need to be transferred into concepts verses black and white. A child can be held to a rule, but how much better when they can apply the concept to their own life beyond the specific application.
Still, there is no magical age this transfer happens at. For example, modesty, two of my daughters have no desire to wear anything that is immodest, while one still desires to wear things just because they are cute, without weighing if it is modest. Until she grasps why we want her to be modest, we will “help” her be modest by watching what she wears.
It may appear legalistic for us to make rules about attire, but we are not just enforcing rules we are also speaking why. Rules alone ARE legalism, but rules along with heart nurturing is allowing a person to mature into understanding.