I joined a forum in around 2012, however, I started to post regular on forums since 2015. I haven't counted how many forums I have posted on but I guess the number could be more than 100. I am passionate about forum posting.
I would think you're on more than 100

Even though I started getting on forums in the late 90s/early 2000s, I think around 2009 and up is when I started posting on them more and more, and falling in love with them more.