Here's why:

* Seafloor Spreading: Mid-ocean ridges are where new oceanic crust is created. Magma from the Earth's mantle rises to the surface, cools, and solidifies, forming new seafloor. This process, called seafloor spreading, pushes older seafloor away from the ridge.

* Continuous Formation: As new seafloor is constantly being formed at the ridges, the rocks near the ridge are the youngest. The farther away from the ridge you go, the older the rocks become.

* Evidence of Age: The age of seafloor rocks can be determined by studying the magnetic striping pattern on the seafloor. This pattern reflects changes in Earth's magnetic field over time.

Therefore, the youngest seafloor rocks are always located at the active spreading centers of mid-ocean ridges.