Pornhub launched in 2007 according to Wikipedia. Mindgeek (Pornhub's owner) had a reported $460 mm in revenue in 2015. (https://www.luxtimes.lu/en/luxembourg/mindgeek-porn-empire-r...) Pornhub is privately owned, so how much of that $460 mm is Pornhub vs other properties is unknown, but Pornhub having made a billion dollars over its 14 years doesn't really seem that far fetched.

Digging a bit more, I don’t think so. The company that owns PornHub does about half a billion dollars per year in revenue: https://en.m.wikipedia.org/wiki/MindGeek

That includes revenue from other brands too, but I believe PornHub is their top brand, and likely accounts for a good portion of that. Also, how much money flows through PornHub that doesn’t count as revenue? I don’t know much about their business model, but say if a content creator generates $100 in total revenue on PH, and $40 goes to PH while $60 goes to the content creator, I’d guess that’s $100 in payments processed, but only $40 in MindGeek revenue?

Based on that, I’d estimate the volume of $$ flowing through PH at somewhere around $100,000,000-$1,000,000,000 annually. Even on the low end of that, around a billion should have flowed through them so far, over the lifetime of the site. And I think multiple billions is quite possible.