Cousin Sleepover

My cousin and I were close growing up and this happened when he was 13 and I was 17. I had a pool in my backyard and he had come over with his younger sister to spend the night while his parents were out of town. On arrival they both wanted to swim right away; his sister grabbed the bathroom across from my bedroom to change in, while he waited in my room for her to be done. I was going to change in my bedroom, so I suggested that he just change in there. I knew I'd have to make the leap here, to get him to be comfortable, so I lifted my shirt over my head. I had a decent body (at that time lol) from running cross country and swimming. I had hairy armpits and a happy trail running from my belly down. I saw my cousin looking at my hair. I put my thumbs on both sides of my waistline and took off my shorts and boxers. I was now standing nude in front of my cousin; my penis was semi-erect. His eyes bulged at the size of my late teenager cock, about 7.5 inches of meat standing out of a full bush of brown hair, with hairy balls hanging low behind. 

He said, "Whoa, dude your dick is massive and your pit hair looks nice." "Haha thanks. Are you going to change? Don't worry, we're both guys. Plenty of guys of all ages change together." He lifted up his shirt slowly. I just pretended to walk around looking for my trunks, my cock wobbling back and forth. I turned to look at his 13 year old nude body. He didn't have any hair under his armpits, but he had a pretty full bush and an already erect 6 inch boner with his foreskin covering most of the head. I wanted to encourage him so I said, "Hey nice, I bet you're pretty popular with that at your age!" "Thanks, man, not as popular as you, I'm sure." I actually didn't have penis in vagina sex until the next year, but my dick was pretty popular with me! We put our trunks on and went outside shirtless. 

His sister was wearing a bikini and had about b cup boobs. We were playing a bit and she shrieks that I had a boner. Her brother actually pulls down his trunks and shows that he has one too! So I followed and took my trunks off and said I'm skinny dipping. My cousin says me too! And tells his sister she should join. It was twilight at this point, so she couldn't be worried about neighbors seeing us. She slowly unhooks her top while calling us gross. Then she lowered her bottoms and tossed them near our trunks. Her body was amazing! She had perky tits with big areolas poking out and a small fuzz between her legs. We swam into the night until my female cousin got tired and went inside. Us boys decided to go inside too, totally naked. I was feeling pretty bold and asked him if he jerked off. He smiled and said yes. I took my penis in my hand and started rubbing. He started too. We both sat on the couch. He moaned and  shot out three globs of cum on his belly and bush. I orgasmed soon after, leaving a pool of semen on my belly. We went looking for towels and ran past my younger brother, wide-eyed and staring at our nude bodies! 

We continued masturbating for years and sometimes included my younger brother and his younger sister. Good times.