Identify the predicate nominative in the following sentence.

astonishingly, the young woman was elected mayor at the age of 25 and became one of the candidates for governor only a few years later.

mayor

one

candidates

governor

i wanna say governor

Predicate nominative is a word or group of words that follow linking verbs.
They explain the noun or rename the noun.

Ex:  Bill Gates is a well-known businessman and philanthropist.
Bill Gates is subject
businessman, philanthropist are the predicate nominative

Astonishingly, the young woman was elected mayor at the age of 25 and became one of the candidates for governor only a few years later.

Your answer would be mayor because it follows the linking verb WAS and restates the subject woman.