I remember pop-up porn adds started to appears around 1995 or so and 1995 is 30 years away...

I ember them showing up and then being limited to super shady sites PDQ.

Which makes sense- since exposing minors to pornography was a crime, and got even more illegal somewhere in that time frame, along with the web becoming "professional" (whitehouse top level domain mixup stories anyone?), the honest pornography sites all started self-regulating and asking if somebody is an adult before anything naughty gets shown.