All you need to be eligible is to be born between 1 July 2001 (included) and 31 December 2003 (included), be a citizen of the EU, have a valid email address, and hold a passport or national ID card.
According to the DiscoverEU website, “As an 18-year-old citizen of the European Union, DiscoverEU offers you the opportunity to participate in a travel experience that will enable you to take advantage of the freedom of movement throughout the European Union, explore the diversity of Europe, learn about European cultural heritage and history, and connect with people from all over the continent. Furthermore, DiscoverEU enables you, as a young person, to develop life skills of value to your future, such as independence, confidence, and openness to other cultures.”
The successful applicants will be able to explore the European Union between 1 March, 2022 and 28 February, 2023 for a maximum period of 30 days, which is plenty of time to have the experience of a lifetime.
Although Interrail is all about train travel, the lucky winners of the free Interrail passes will be allowed to ride ferries, coaches, and planes if needed. 
A version of this article was previously published on February 22, 2021, and was updated on October 13, 2021, with more information.