Vbulletin question

hey there, im not sure if this is the right place to post this question, i searched the forums on vbulletin and most of the threads were posted in “Random” if its in wrong forum, Admin/Mods, please move to respect forum…thankyou

I set up a vbulletin forum… Here is my problem, i need to set the age requirement to a set ae, ie, 15 for registeration. but i know that people can simple go back and re-enter a fake birthday and be allowed to register,i know its hard to monitor this but at least it will help alittle bit. is there a way that anyone knows or is willing to share/help me in fixing this? im running the vb3