I am personally celebrating my 30th anniversary of reenacting.
Hooray for me!
Most of the people I hang with have about the same amount of time in.
Fwiw, our lineage goes something like this. A bunch of people in the medievalist group I was once a member of held a feast many years ago (circa 1985), the theme of which was Pirates, as opposed to the normal Vikings, Saxons, Normans, etc. It was so much fun, it became a yearly thing. Each year, after it was all said and done, we'd kick back and say, "you know, we should actually reenact this period." Fast forward about 5 years, and most of us had migrated into RevWar. But every year we'd still go to the Pirate Feast. And every year we'd say "you know, we should actually reenact this period."
About 1994 I decided to do something about it. I made my coat. Started talking to some others. A bunch of us got together with a notion of putting together a camp for Military through the Ages. I was quartermaster. Joe Marek was captain. The lot of us went down to Jamestown for the event... and lo and behold once there we were told "pirates aren't military so you will not be allowed to participate." This was about 1995. May have been '94 or '96. But anyway, that's the first time I know of that someone got together to make an attempt at "reenacting" pirates, in the sense of the term as I am familiar with it.
I know people have been dressing as pirates in one fashion or another and celebrating the pirate ideal for much longer.