My younger sister and I have been in a monogamous relationship for a few years now. I am 40, and my younger sister is about a year and a half younger than me. I know it may gross a lot of people out, but we are in love with each other in ways most people only read about, and we couldn't be happier. I'd be lying if I didn't say it wasn't erotica and taboo doing my sister, and finishing inside her knowing their might be a slim chance she could get pregnant.