There’s no hard and fast rule that says how old a console needs to be for it and it’s games to be considered retro.
There are a lot of people that say that anything from two generations ago is retro. That would put the PlayStation 3, Xbox 360 and the Wii in the retro camp.
Do you think the PS3 generation is retro or if not what consoles do you consider to be retro systems?
You can also still download and play 360 games online. With Microsoft still maintaining the infrastructure (like for various Call of Duty’s).
You can go download Super Mario Bros, too. That’s probably not a great bar for it.