I would hazard a guess that they’re using google analytics to collect this data, and google is creepy and knows everything. Maybe they got you to tell them your age at some point, or they can use the vast amount of other data they have to estimate it with probably-super-creepy accuracy.
By the way, how can a site know your age through mere non logged in access?
You don’t have to be logged in because you’ve got a digital fingerprint.
I would hazard a guess that they’re using google analytics to collect this data, and google is creepy and knows everything. Maybe they got you to tell them your age at some point, or they can use the vast amount of other data they have to estimate it with probably-super-creepy accuracy.