[Vocabulary] in his/her years // in his / her ages?

[englishhobby]

What is the correct idiom describing an elderly person?
She is in her ages. - Can I say so?
He is in his years. - Is this sentence correct?

I couldn't find idiomatic or set phrases related to old age in dictionaries (I found "to be in one's golden years", though. But should "golden" be always used? Can't it be omitted?)

 

[emsr2d2]

What is the correct idiom describing an elderly person?

None of the words in your title are idioms. You can say that someone is "in his/her dotage", or "is aged" (pronounced with two syllables). Generally we just describe elderly people as "elderly" or "old".
There is a rather unpleasant idiom which my grandfather always used for very old people - "coffin dodger".