Ever since I can remember my step-brother and I were taking showers together. I am two and a half years older than him. Shortly after I started grade seven, I think I was twelve, I had started to grow some pubic hair and my brother David had started to take notice.
One morning I had wood and sheepishly got into the shower after the alarm went off. David noticed and after about 30 seconds in the shower he reached out and grabbed my cock and started stroking it up and down. I had never masturbated and was a little shocked when he started but after my initial surprise I started to feel really good and eventually I blew my first load, the feeling was incredible.
Afterwards, he told me that his best friends older brother George had taught them how to masturbate the week before. He said his brothers penis was almost twice the size of mine. This peaked my interest and another day jerked him off, but that is another posting.