No, grandma isn't a closet dominatrix, if that's what you're thinking!
A geek type guy, early twenties, perhaps younger, begins small with an idea of creating a website and taking pictures for an escort he's fallen for, a website that showcases her 'goods' and services. He does a good job and gets paid in freebies. Soon more girls, friends and acquaintances of the first come to him for their own website and his burgeoning photography skills. Jealousy and rivalry ensues? Before he knows it hot young girls are coming and going out of grandma's house to visit her grandson. Things get increasingly awkward, uncomfortable and harder to maintain. Will our intrepid geek have to give it all up or will the once shy and awkward young man open his own studio?
While this could possibly go group play, I wouldn't see more than three players in all. Ideally myself and one other reliable, committed writer would be preferred actually. Meaning you may have to play more than one role, or multiple characters. Grandma would be an NPC.
A hetero story idea from Zamdrist? <gasp!>