Retro means modern games that remind you of old games. Like Shovel Knight or UFO 50. There's not really a time limit to that. Shovel Knight is quite old now, but the graphical style it copied is even older, so it's still retro.
Obviously, I'm sort of joking, but y'all do use the word "retro" wrong. You're talking about vintage games, not retro games, and yes, I will die on this hill. Gamers are the only people who don't know the difference between retro and vintage. Everyone else gets it right: car people, clothing people, furniture people, sneaker people, jewelry people, etc.