The Atlantic Ocean is show in the middle. Under which parts of the Atlantic ocean is the oldest sea-floor rock?

Since the crust is formed along the mid-Atlantic ridge, the oldest seafloor rock would be found near the coasts of either continent to the left or right of the mid-Atlantic ridge. 

Seafloor spreading is the process by which new oceanic crust is formed along the mid-Atlantic ridge. Along the mid-Atlantic ridge, convection currents under the mantel cause the tectonic plate of a divergent boundary to move apart from one another. Such movement may also result...

Since the crust is formed along the mid-Atlantic ridge, the oldest seafloor rock would be found near the coasts of either continent to the left or right of the mid-Atlantic ridge. 

Seafloor spreading is the process by which new oceanic crust is formed along the mid-Atlantic ridge. Along the mid-Atlantic ridge, convection currents under the mantel cause the tectonic plate of a divergent boundary to move apart from one another. Such movement may also result in earthquakes and volcanoes. As the plates move apart, the churning magma of the convection current wells up between the divergent boundary and moves towards the surface of the seafloor. Once exposed, the rising magma cools. Thus, seafloor spreading is speculated to cause continental drift and the creation of new crust.