If you're happy to accept the Manifesto in 2001 as the start of agile, then https://www.scrum.org/about https://www.scrum.org/about under 'Creating Scrum' state

If you're happy to accept the Manifesto in 2001 as the start of agile, then https://www.scrum.org/about https://www.scrum.org/about under 'Creating Scrum' states "Jeff Sutherland and I had been using Scrum for ten years prior to the meeting at Snowbird where we and others signed the Agile Manifesto"