This is the 3302nd most frequent French word.
trentenaire
A "trentenaire" is a person in their thirties.
Here, 'trentenaire' is used as a noun to describe a person in their thirties.
Je suis un trentenaire passionné par l'histoire.
I am a person in their thirties passionate about history.
In this sentence, 'trentenaire' is used as an adjective to define the decade of someone's age.
Être trentenaire est une étape importante dans la vie.
Being in your thirties is an important stage in life.
Here, 'trentenaire' is used as a plural noun referring to people in their thirties.