My first bi experience happened a long time ago when I was of an age I will not specify. My best friend at the time had an older brother, in his mid 20s, who lived in an attic apartment. One afternoon, he invited me and four of my friends up and started showing us nudie magazines. About a week later, he invited us up again. This time he had some hard-core porn magazines. He convinced us to masturbate and showed us all how. Several days later he showed us how to do a "Circle Jerk," where we jacked off the guy next to us.
After we have been doing circle jerks on a regular basis, he invited me to come up to the attic one day alone. He had me drop my trousers and showed me how to give a blow job. He sucked me until I exploded in his mouth -- then coached me through giving him a BJ. He waited until his cock was well down my throat before he came and I ended up swallowing his whole load to my surprise.
These kinds of meets continued through summer until we began school again. At that point one of the guys came and told us what we were doing was "Queer," and that if anyone found out we all be screwed. After that we never did it again. But wow did I have fun that summer. It never occurred to me that the older guy was "grooming" me and truth be told, I really enjoyed the whole thing.