The Furaffinity synopsis of the story says that Jamie is 18.

Also, most bathroom locks have a way to unlock them from the outside, in case of emergencies.

Additionally, Jamie is single whereas Jamie's mom is quite married. Michael seems like he's probably not so inclined to think with his dick - he was put in a rather awkward situation when Jamie crawled under the table and began licking him. It wasn't exactly like he could say, "Um, your daughter is under the table and about to give me head."

This is reasonably good storytelling. I'm looking forward to seeing what's next.

Also, cute ass. :3

This is an erotic fantasy story. Things often happen in them that breach all manner of real-life decorum.