What is age classified as?

Age is classified as nominal data.
Nominal data is a type of data that is commonly used to name variables. They can have numbers assigned to them just like ages, the pinned number on a sport person. Nominal data are categorical and they belong to a specified category.

Ordinal data tells the position of something in a list, you cannot do arithmetic with ordinal numbers, and they are only used to show sequences. Example of such is: first, second, third, and fourth.

Interval data is used to measure in scales; it is used to measure things between two extremes. Eg On the scale of 1 to 10, what is the threshold of your pain?
Ratio data is used to compare many variables. Eg Mary can be as twice as tall as Jane.