When I was twelve, I was very curious about the opposite sex. I finally worked up the nerve to ask my brother, who was fourteen at the time, if I could see his 'thing.' He was very surprised, 'You really want to see it?' I assured him that I really did.
He was unsure at first, but seemed very interested. After promising that I wouldn't tell anyone, he finally agreed to show me. He unbuckled his pants and pulled them down, and I was amazed to see his hard penis bounce up as his shorts came down. I stared in fascination, and hestitantly reached out to touch it.
He moaned slightly, and his penis twitched. I looked up at him and he said it was ok, it felt good. He asked if I wanted to see it 'squirt.' He gave it a few pulls and asked me to take over. I stroked his cock, and he asked me to hold his 'balls' gently as well. It didn't take long at all and he was shooting cum onto the floor (and some on my hand). Afterwards he seemed nervous and quickly pulled up his pants, making me promise again not to tell anyone.
He wiped the floor, and after I quickly sniffed the cum on my hand, I wiped my hands off too. We never did anything like that again, but I often thought about it when I masturbated after that.