How did Mount Evans become a mountain?
Just to elaborate on David Hammen's correct comment:

The granite is old. The mountain is fairly young. There is no
contradiction

Mountain belts like the Rockies are built by tectonic forces. Two plate collide, and mountains rise in between. The material that makes up the mountain does not have to form during the collision (although it sometime does).
A &quot;batholith&quot; is just a collection of many granite intrusions, which are mostly underground. They do not have to be mountainous. In most cases they are covered by sedimentary rocks and you don't even know they're there. They only become mountains when you &quot;fold&quot; them. When you fold a piece of paper and it wrinkles, you have to separate the formation of the wrinkles (which happened now) from the manufacturing of the paper (which was in a paper factory, in the past).