I am so thankful I don't have a LinkedIn, Facebook, etc. account to mine for data.
That depends if they know that you visit websites which are also visited a lot by other males between the age group of 20 to 30, then they can almost assume that you are a male between 20 - 30.
No tracking needed. Much better accuracy and return.
The days of just targeting you based on the content site are over, now demographics and your search/click history plays a role too.
Maybe they have a few percent better accuracy than guessing at random. And that might be worth a few billions. But on an individual level they just don't have the slightest clue.
edit: State of the art tracking seems to be "look at what products user x has looked at, show the exact same product everywhere after he/she probably bought it".
Now if you do have and use a facebook account that is another thing.
Can you give some sources for your claim?
I guess the most tangible data point is when google allowed you to look at what google thought if you (gender, age, interests etc.) and how bad they are at it unless you actually use their services.
It is obvious they would be far better of targeting sites than users without accounts. But that is not where their competitive edge is so they downplay that. Also, I guess they are big enough to not care about people without accounts.
They can't even detect fake and duplicate accounts, which would be trivial in comparison.
They almost certainly can, but due to capitalism, they have a business interest in not really removing these accounts.
Messenger asks nicely to upload your whole address book, and since half your college buddies clicked yes they know when and where you studied, and who you knew, and your parents landline thus some idea of their location (and how wealthy it is). Ditto your colleagues at each place you worked, who all still have your old corporate email, and some have newer info...
And that's before anyone posts anything on facebook.
They have the data, yes. But they will ruin society before having any idea on how to use it.
Most importantly. They can not correlate that with my IP or my browsing history. So that information is beyond useless when trying to track me and only slightly useful for researching the society in which I grew up (which facebook isn't interested in anyway).
When I make the mistake of buying something online in a browser logged into facebook, then I get adds for a week trying to sell me what I just bought... this does not lead to me buying another one! And all this strategy seems to need is basic cookies, not a shadow profile.