The original sentence is grammatically correct but could be slightly clearer with some rephrasing.
The meaning of the sentence suggests that the speaker is questioning when it became a practice or social norm for people to associate the consumption of "golden morn" (a brand of cereal) with a person's age. This implies that the speaker finds it odd or unfair to categorize cereal preferences based on age.
Here are some possible rephrasings:
1.


