Addressing people using their desired pronouns can be a challenge if you've known them for a while. That challenge seems to compound with age. Even trans people can misgender other trans people from time to time. I have a small suggestion that has helped me:
About a year into my transition, I was really considering my pronouns, not sure if I wanted to be a "he", "she" or "they." I started to pay more attention to everyone's pronouns, especially those of other trans people, since I joined support groups and online spaces. Sort of organically, I started leaning into "they" as a way of referring to people who I don't know, who've not yet told me how they'd like to be addressed.
The more I did this, the easier it got over time. My goal now is to consider everyone a "they" until they tell me otherwise. That pronoun doesn't seem to offend anyone, it works in regular conversation and it gives them agency over their identity, which is something I think all people deserve.
If you're interested in becoming more flexible with pronouns, I think this practice will help you.