As I read the About Demographics page in the Help (https://support.google.com/analytics/answer/2799357) (Where Analytics gets the data section), I think I understand that the demographics data comes from the Doubleclick cookie or the Android or IOS app. Since the sites I work with have no Android or IOS apps, and we have no advertising on our site, I am concluding the following: Demographic data is retrieved from a user's device based on the Doubleclick cookie already on the device. Is this true?
In the Demographics reporting, it also indicates the percentage of all sessions represented by the demographics figures. This allows me to know the percentage of users without a Doubleclick cookie as well. If the percent of total sessions represented in the Age chart is 51.03%, I can conclude that 48.97% of visitors did not have a Doubleclick cookie at the time of the visit.
Are my conclusions correct as I continue my learning?