What is the noun in sentence No one could believe that Stella took dance lessons at her age?

The noun in the sentence "No one could believe that Stella took dance lessons at her age?" is Stella.

Here's why:

* Stella is the person who took the dance lessons.

* No one is a pronoun.

* believe is a verb.

* that is a conjunction.

* lessons is a noun, but it's part of a noun phrase ("dance lessons").

* age is a noun, but it's functioning as a prepositional phrase ("at her age").

Nouns are words that name people, places, things, or ideas. In this case, Stella is the person being discussed.