https://jasonsiocoblogs.wordpress.com/2020/12/20/its-highly-possible-to-develop-perfect-pitch/
I do however take offense to the comments said by Volcanoadam... ear ageing??? My hearing is fantastic and I have the hearing of a late 20 year old, despite being in my 30's. Non-standard tunings? They're slightly annoying but you adjust.
The good thing about perfect pitch is that while you have perfect pitch - you also have (be default) brilliant relative pitch, so you can accept when pieces are in a different tuning system or in a lower tuning pitch.
I've heard that perfect pitch usually starts to degrade in your fifties (it's often off by a half step)
I don't think that's entirely true. I mean, you don't forget colour - so why would you forget pitch?
Because pitch is stored as long-term auditory memory [...] however, is reliant completely on a specialized auditory memory which is completely in the brain. And apparently, auditory memory of any kind starts degrading in your fifties.
I hope to prove that wrong in 30-40 years.