age compares the age of an object to another.

That is correct. Age is a measure of how old an object is compared to another object, usually the age of the Earth or the age of the Universe. For example, geologists use radioactive dating methods to determine the age of rocks and minerals by comparing the ratio of specific isotopes in the sample to those of a known age. Astronomers use similar techniques to determine the age of stars and galaxies by comparing their properties to those of other objects with known ages.