If you don't talk they don't hear.
Simple as that.
My mom is 80 and on a good day she generally recalls most things. But hey 80 is 80.
She knows I prefer female manners of address, and she knows it bothers me, and she knows I value the acceptance more than some words.
If she goes to her grave never really getting it right, she will pass on knowing I loved her all the more for her accepting me regardless.
Now if a 20 something minor relative or work colleague or casual acquaintance can't get it right, that makes them of limited intellect eventually. The proper response there is 'what? are you that dense? that incapable? do I start referring to YOU in an unacceptable fashion? would you mind being known as doofus?'.
Because our name and manner of address, it's not a 20 digit serial number we are asking them to remember. It's a damned name, and gender.
It's NOT rocket science, it's about them giving a damn to a point.
But hey, I've mis pronoun ed myself on several occasions and been annoyed on the inside. What? do you need sweat running between your breasts on a hot day in a confining bra to remember your gender?

But like I said, if you never say anything, you have no right to complain. People only know it is a problem if you tell them.