Or would it be:
Among 24 to 34 year old women.
Someone may say that they are 50 years old, but are they a 50 "year-old" or a 50 "year old"
Is there a standard rule about hyphenating?
If the phrase comes after the noun, it is not hyphenated:
The women are 24 to 34 years old.
"Fifty year old" (or 50 year old) in the sentence as you used it is a compound noun. I don't believe you need hyphens in that sentence.
She is a 50 year old.
But
She is a 50-year-old woman.
And
The woman is 50 years old.