How old does a game need to be to warrant a remake?

[Wman1996]

Well, not many remakes are ever "warranted".
I would say most remakes need a bare minimum of a console generation (5-8 years), but two console generations (10-14 years) is usually a better idea.
If The Last of Us didn't get a PS4 remaster in 2014 (only a year after its PS3 release), I could understand remaking it already in the early 2020s. But the PS4 release in particularly has aged very well, especially when you play it on a PS4 Pro or PS5.
Xenoblade Chronicles got a remake 10 years after its initial Japanese release, 9 years after the European release, and 8 years after the North American release. Considering that game was so held back graphically by the Wii, more than enough time had passed.
A lot of Xbox 360, PS3, and Wii U titles don't really "warrant" remakes yet. But the Wii, 6th generation consoles and earlier? Go for it. I'd like to see more fifth generation remakes in particular.