I think you should maybe just chalk this up to a generational difference.. While some older people are capable of understanding the need to treat medical transsexualism or even the transgenderist cultural movement, for many, its just too far out of their realm of understanding. My Grandmother (92 years old!!) was totally fine and actually fascinated by the medical side of things, yet still misgendered me lol... when I mentioned this to her, her response was "well, I changed your nappies(diapers) and I remember what I saw" So, her understanding wasn't total but she tried.. Just like I tried not to get hurt when she slipped up.
Acceptance from older people will come down to a lot of specific cultural factors. Imagine where the older generations grew up, the world has changed a huge amount in a very short time. the civil rights movement in the US was only 60 or so years back, slavery was legal there around 150 years back.. and racism still plagues that nation. A lot of western democratic nations are slowly waking up from institutionalised bigotry that has kept every minority you can name oppressed. It takes time. Be patient with the older generation but keep in mind they'll be dead soon anyway, their bigotry will die with them, but so will the things we loved about them. Take some time to read about their part of the world, and the cultural time frame they grew up in, you might find you're not so hurt when they make mistakes if you understand the world they came from.
I can almost promise , when you're their age, the kids will be doing something you don't understand or agree with...
