For chronological accuracy, I have been using the old name and gender when referring to a past, pre-transition person, and the new name and gender when referring to them generally.
But I had a realisation that this could be considered rude. I’d like to hear from some trans people on their opinion.
Just ask them, I think the more popular consensus is that you use their modern information, but I personally would actually prefer that people use my old information when talking about my younger self. So everyone has their own preference and you should check with them first