Here's the thing: Like used said, everybody is wrong.
Retro doesn't mean old. Retro means it's in the style of old. Pac-Man, Tetris, and Pong aren't retro games, they're old games (Or, if you want to give them some more credit, they're vintage games). They can also be considered classic games (more on that later). Super Meat Boy, Lone Survivor, and other new games with those old school graphics and mechanics are retro, because they aren't actually old games, they're just acting like it.
Classic, on the other hand, has a much wider definition. It can mean original or very old, it can mean serving as a standard, it can mean it has enduring quality and appeal. Pong is a classic arcade game, because it has been around longer than the rest. Doom and Goldeneye are classic games because virtually every FPS every made has been influenced by them in some way. Tetris is a classic, because it is so widely played and acclaimed. That E.T. Atari game that is widely seen as the worst game ever made? It's a classic because its fucking old. I would go so far as to call GTA 3 a classic, because even though it is from the PS2 generation (which makes an ancient-in-gaming-terms 11 years old) everybody played it, it was met with near-universal acclaim, and its open-ended world structure has been imitated countless times in countless ways.
So, to recap:
Vintage is old, retro is acting like its old.
Classic means it has earned special status or recognition, through its quality or its age.
Classic games are not retro games, but retro games may someday become classic games.
