Lowest age possible for site members...

Lowest age possible for site members...

How can I make this default lower than 18? I have tried to adjust the values in the "Advanced Settings" but still the change did not took affect with the sign-up form. Wish somebody help me on this. Thank you.

you have to do that also into the fieldbuilder - join 
Clicj on day of birth go to the advanged tab, and change there also the minimum and maximum  age and save this