If when trying to use Cortana on Windows 10, you receive a You're not old enough to use Cortana message, then it simply means you are not old enough!

The age, on the Microsoft account profile being used, needs to be 13 or older.

You will have to ensure that the age you mentioned while creating the Microsoft Account you are using for Windows 10, make you 13 yesrs or older.

This is because it is illegal for information on young children to be acquired for anything involving an internet search, according to the Children’s Online Privacy Protection Act.

Windows Phone users may receive a I'm sorry, you'll need to be a bit older before I can help you message in such a case.