In my opinion, the advertiser should not know that the current visitor is an 80 year old grandmother in the first place.

Just like TV, radio, and magazines before them, advertisers can select which advertisements to put on which sections of websites (or broadly make their decisions on what types of sections they should display on), and individual display requests can and should be de-personalized for privacy measures. Advertisers can still access or determine indicators of demographics for places on the web without individual tracking measures, and measure click-through for various A/B testing for different ads in different contexts.

The contents & general audience of a page should determine the ad, not the individual visitor.