In the Atlantic which part of the oceanic crust is younger

Oceanic crust is younger crust. Well, It is because, an oceanic crust is formed when a continental crust undergoes a big tension crack due to the forces generated inside the earth, which may be because of the magma dwelling inside. As the crack becomes prominent, the continent is broken into the segments with a big oceanic basin kind of structure between them (This takes millions and millions of years). Sediments deposit in the basin and get stratified to form the oceanic crust. This is the reason that oceanic crust is younger than the continental crust.

The oldest crust is about 260 million years old. This sounds old but is actually very young compared to the oldest continental rocks.