Nice USE of granny. Mouth fucked a granny (in her 80s) when I was in my 20s. She swallowed every drop. Grannies know what their mouth is for and how to swallow.
That's the way it should done, doesn't matter what age the cockslut is. Hands cuffed behind back, nipples clamped (I prefer weighted, tight clothes pins) and keeping the cock in her mouth until you've been drained. Of course it's always good if she's made to service several cocks in the same session.