I'm sorry Byakuren.it seems the fandom has pretty much decided on that,but don't worry,I still love you..:3(plus,you had all that youkai girls harem who practically willing to die for you..)
she actuall fits very bad in the granny squad exept for her being old she has no point matching exept bing a final boss or ex boss yukari yuyoko kanako and eirin look old (while in yukaris and yuyukus case its just the hat wjho makes the old look) byakuren only looks adult like yuuka komachi or yuugi who surly have around the same age
if its just for those reasons you would turn suika and yuuka in "grannys" too i dont think suika will care about that but yuuka will kick everbodys a** who call her granny
I'd figure Byakuren to be among the more youthful of the group, along with Yuyuko (Stuck in her very well developed teens), and Yukari (Is 17) in contrast to Kanako and Eirin.