That is a strange way to say she’s 57…

But anyway! Range varies wildly with age. 6 years is something you at least ponder at age 25, but will feel like “same age” around 50.

My feeling based on what people seem to at least not care to even gossip lightly about: max 1 year at age 15. 5 years at 40. 10 years at age 60+.

Wider ranges are not problematic, but gets into at least “interesting to talk about”. E.g. “They are 33 and 40! Huh! Good for them.”