Kinda just a discussion

Okay so I've been thinking about the roles females play in ballbusting stories like who they are to the main character and I'm not saying I'm necessarily interested but I've realized something... There are not many grandmas
I see mom, sister, classmate, roommate, cousin, aunt, coworker, girlfriend, wife, "in law" , sister of ___, random stranger, Dominatrix, and probably a few more that I can't think of ATM. But I don't think I've ever read a story where the grandma bust valls