Forgive me for my confusion, but what pronouns and name should I use when referring to a trans person's childhood -- especially in a story that is from the perspective of someone else in that person's life? Should I use their current name/pronoun even when telling a story that happened at a time when they were using a different name and pronouns?

Here's an example:

Recently, I was telling a friend of mine about how my aunt and uncle chose a preschool for my cousin. My cousin recently switched to she/her pronouns, but grew up using he/him pronouns. So in my story I think I said something like, "my aunt and uncle ended up choosing [school name] for my cousin because they felt like it was a safer and calmer environment for him." It felt normal to use the pronoun "him" in that instance, since I was talking about a time in my cousin's life when they were living as a boy. Furthermore, since I was talking about my aunt and uncle's perception of the best preschool environment for my cousin, it seems like if I had used the pronoun "her" I would be implying that my aunt and uncle knew that their son was really a girl when (at that time) they didn't.

Does that make sense?

Is there a hard and fast "rule" for how to handle these kinds of situations? Or does it all depend on context? Normally I am pretty good about adjusting to new names and pronouns, but this situation kind of confused me.

Edit: Thanks folks! Sounds like the consensus is that I should default to using the current pronouns even referring to stories from the past.

I should maybe clarify that I would never out someone to a person who I didn’t know to be trans-friendly. The person I was talking to in this context was also trans — and does not know my cousin.