Here's why:

* Seafloor spreading is the process where new oceanic crust is created at mid-ocean ridges. Magma rises from the Earth's mantle, cools, and solidifies to form new crust.

* As the plates move apart, new crust is continuously formed at the ridge, pushing older crust away from the ridge.

* The further you move away from the mid-ocean ridge, the older the seafloor rocks become.

Therefore, the youngest rocks are right at the source - the mid-ocean ridge.