I'm probably the oldest person here, though not the oldest watcher.
I was watching the East Blue saga on TV with my eldest daughter when she was about 11 or 12, it was around 2008-2009. Then the TV channel was sold, One Piece stopped airing in my country and I forgot about it for several years. Then my younger son discovered the series online in 2014 when he was 13, and we decided to make this series a quality time between mother and son. We watched it together one episode a day for two years (for him it was a rewatch). When we got to CP9 arc I was already watching for myself, not only for my son, and when we got to Marineford I fell in love with Ace and became more addicted than him. I reached the ongoing episodes at the end of dressrosa, in 2016, and couldn't just wait for a whole week at a time without doing anything about my favorite series. So I joined a fansub, and then established a project of translating the manga to Hebrew. It is what I do for a hobby since chapter 814 to this day.