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.
WhatsApp, which is owned by Facebook, will ask European users to confirm they are at least 16 when they are prompted to accept new terms of service and an updated privacy policy in the coming weeks.
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.Other changes announced by WhatsApp include enabling users to download a report detailing the data it holds on them, such as the make and model of the device they use, their contacts and groups, and any blocked numbers.
WhatsApp, founded in 2009, has come under pressure because of its end-to-end encrypted messaging system and its now suspended plan to increase the data shared with Facebook so adverts could be more effectively targeted.
Facebook is under scrutiny from regulators and lawmakers around the world since disclosing last month that the personal information of millions of users wrongly ended up in the hands of political consultancy Cambridge Analytica.