^I feel it’s more subjective.
Especially, if one feels that they have or are declining in health.
I have to admit, I have never said “back in ‘my’ day.”
“Back in the day,” to me, has a spectrum.
There’s “back in the day” – “waaayyy back in the day.”
The longer I say “way,” the further back in time.
I wasn’t alive wwwwwaaaaaaaaaayyyyyy back in the day.
But. I remember way back in the day, when I trusted my government.
I may also add things like way “the fuck” back in the day.
Occasionally, I will say something was “back in your days.”
Some days, are just “not my day.” Or, in my life, not my year, not my decade, etc.
If I’m dead, I can’t say “back in my day.” So. Your context, is off.
Unless you are hearing me talk, through a Ouija (“weegy”) board.