Users of the popular instant messaging service currently have to be at least 13 years old, but the company is enforcing stricter rules ahead of the introduction of new data privacy rules in the EU next month.
It is not clear how it will verify answers from users, given the limited data requested and held by the service.
WhatsApp, which had more than 1.5 billion users in January, said in a blog post that it will not be asking for any new rights to collect personal information in the agreement.
Facebook, which has a separate data policy, is taking a different approach to users aged between 13 and 15.
It will ask the teenager to nominate a parent or guardian to give permission for them to share information on the platform.
If permission is not provided, the user will not see a fully personalised version of the social network.