When I was a teenager, my refractory period was maybe a minute or two. I could easily knock out two or three orgasms in about 10 or 15 minutes without working up a sweat.
Now, about 25 years later, it's about 10 minutes between orgasm and ready-to-go-again, but I'm happy to say I'm still able to play a doubleheader. It takes longer to shoot that second load, though. That's why I like to get the easy one out of the way first when I'm with somebody -- because the second one will take a while and that gives us some time to play.
That said, I had a chance encounter last week with an absolute expert cocksucker -- all he wanted to do was suck my cock, without reciprocation -- and he managed to get me off twice in 10 minutes. The first one was a quick surprise but the second one was entirely because of his skill. Needless to say, I felt like I was 16 again ... except for the fact that I was absolutely spent, my knees were shaking, and I couldn't get up off the couch for a good 5 minutes.
I've experienced that one other time since reaching my late 30s -- a guy gave me a great blowjob, made me cum in his mouth, swallowed while keeping my cock in his mouth, and then resumed sucking while I was still coming down off the high of that first orgasm until I blew my load five minutes later.
Cheers,
DL