I would like to have the more information about how Adode target know genders and ages from the new visitor(first time).
Adobe Target does not capture the customer details itself until it is passed in mboxparameter through website implementation
How to pass parameter in global mbox > Pass Parameters to a global mbox
If you are already capturing this data in your 3rd party database, you can integrate it with Adobe Target through customer attributes
For more information on customer attributes , you can visit a training and documentation below https://helpx.adobe.com/customer-care-office-hours/target/customer-attributes-its-best-practices.htm...
Adobe Target: Customer Attributes and its best practices > Training
Customer attributes > Documentation
Hope that helps and addresses your concern.