No Mutants Allowed

It's relative. I consider anything more than 2 generations old "retro" but that doesn't mean "retro style gameplay" in my head.

It's just one of those things that doesn't have a concretely defined and widely agreed upon meaning.

Mario with limited amount of lives.
No save points or limited save points.
Sidescrolling.
Turnbased.
Requires a brain to play.

No "take cover" function

No save points or limited save points pretty much disappeared with the SNES era. There were some games with limited saves like Reisdent Evil but it was very uncommon even back then. The first Legend of Zelda was one of the first console games to have saves.