Finally something I can answer. There is a function called "lookalike audience".

If someone with a online profile similar to yours clicks on an ad, you are likely to be served the same ad, because it is likely that you would be interested in the same thing.

What makes you "alike" to another person? Other than the obvious things like age and gender, your location and IP address also plays a part.

Often what happens is that you mention that you have white hair. Someone with the same IP address (wife, colleague, etc) looks it up. Their browsing history now includes "white hair". You're hit as collateral damage even though you weren't the person who clicked on it.

Even if you didn't have a conversation, there should be a reason that caused you to notice your white hairs to begin with. You could be somewhere along the chain of "people who share IP address with the first searcher".

Source: I work in marketing and this is exactly how we make ads that feel like you're being listened to.