Is the youngest part of a rock from the bottom up or from the top to the bottom?

How do scientists tell how old a rock is other than that?

Rocks are looked at by the shape to see how old they are And the youngest rock is at the top where it forms

The youngest part of a rock is always on the top as the oldest is on the bottom.

Scientists look at the color and the form of rocks to also determine how old a rock is

Studying rocks are boring so I don't really find them interesting