Yes, I had some pages on geocities around 1996/97 and to the best of my memory they had no ads. I must have stopped using the site entirely by the point they got added.

edit: Wikipedia claims that happened in May 1997.

That's exactly right. They were REALLY chill in the early days: "The only code that we require to be on all of your html pages is a reference back to GeoCities. This can be a reference to the main Neighborhood page that you reside in, or to the GeoCities Home Page. Please see the FTP Procedures Page for the preferred source code." from https://web.archive.org/web/19961220170537/http://www.geocit...

The other rules are actually pretty cool, too. Zero commercial use allowed. This probably singlehandedly ensured the most diverse and interesting content.