At Control Magic, here is how we define Standard, Modern, and Vintage Cards.
Vintage decks may consist of cards from all Magic card sets, plus the following cards: Sewers of Estark, Mana Crypt, Windseeker Centaur, and Nalathni Dragon.
Standard decks may consist of cards from recently released Magic sets (roughly the last 2 years). Currently those sets are: Dominaria United, Streets of New Capenna, Kamigawa: Neon Dynasty, Innistrad: Crimson Vow, Innistrad: Midnight Hunt
Modern decks may consist of cards from Magic card sets going back to Core Set Eight and Mirrodin in 2003 through today.
Source: Wizards of the Coast