age problem

Hi i want everybody to join my social netowork but i people who is  under 18 cannot join my social network but why? is there any way i can change it? I try to change it but i cannot.First i clicking on setting then Advanced Settings and i found something says Lowest age possible for site members and i change it to 15 but it didn't work. Can someone help me plz

You must also Go to:

admin > Builders > Fields Builder

Click on 'Date of Birth' item, then 'Advanced' tab

Make sure 'Mandatory' is checked, Enter 15 for 'Minimum Value' and whatever you want for 'Maximum value'

thanx