Big Brothers/Big Sisters

So I volunteer for Big Brothers/ Big Sisters of Huntingdon and I've been mainly just assisting to the main supervisor. I've learned the way for matching up Big Brothers/Big Sisters and recently learned something new about the pair up process. Big brothers and sisters are matched up with a little brother or sister, but there is a rule that big brothers can only be matched up with a little brother, not a little sister. Big sisters can be matched up with a little bother or a little sister. Isn't that crazy? I do understand some of the reasoning behind it but i'm just surprised such a well known organization can be so obviously sexist. And I know it's for the safety of the children so young girls don't get pressured by older boys but an older girl could just as well pressure a little brother. You can't just assume in either circumstance what could happen.