Penises don't come with a size label on them so how's a boy supposed to know? Looking at porn you might be forgiven for thinking that they're all eight inches long.
A Story in the SWMS (Dimension 69) Universe
This is a story, about a young man named Joshua, and his twin sister Heather. He has two older sisters named Becky and Rachel all who live with his mom. He doesn't know who his dad actually is, but on one hot night, while his elder sisters are at college, he and his twin sister start something, something that blows into an out of control, piss your pants, awesome adventure.
A Star Trek Fan-fiction Story
It was Wesley Crusher's last night aboard the Enterprise and one other member of the crew was determined to make sure that it was a memorable one
Howie a 16 year old, is upset when parents separate and takes off for NYC and his sister. They have a border-line but not quite incestuous experience and she introduces him to Candy, her very horny girlfriend.
Accidental Lovers is a story in three parts, each part can standalone, but all come together in the end. In the first part, young Tommy Roberts is bedridden after an accident, and must be cared for by his younger sister. Curiosity gets the better of both teens and soon their homeschooling becomes a hands-on lesson.