How old are you if your parents fucks you in the bathroom? If you are an old man or woman who had sex with your parents or someone who is just old enough to have sex, then it might be time for you to consider the possibility of a threesome. Threesome is defined as "a group of more than two people" and could be described as a couple having sexual intercourse together or it can simply be two people in love with each other. To clarify, a threesome is not a threesome with his parents; it's simply a threesome consisting of two people..