I was 15. My bro was 13. I was just short of six feet and my dick was probably about six inches.
When I was 15, I had been jacking off for several years. I did it pretty much everyday and it was a big part of my life. I would sit on my bed stroking my dick thinking about the girls at school or church. One day, my little brother Albert walked in on me jacking off. I tried to hide, but he said he wanted to know what I was doing. When I told him I was jacking off, he said he knew what it was but didn't know how to do it. Being the great bro I am...and the horny one who really just wanted to cum...I offered to show him. I pulled my dick back out and came relatively quickly. I came in a way that I coated my cock and balls with jizz.
When I was done, my bro started to try to jack himself off in front of me but he had some trouble, so I helped. I took some of the cum on my balls and used it as lube to jack him off. When he was done, which was fairly soon, I took his cum, joined it with mine, and jacked myself off again because I was so horny. I shot another big load, this one on my stomach and I took it and used it to give Albert another handjob. After that, we were both covered in cum so we both showered.