I feel like the pianist trained you rather than you achieving it like a little kid does. That happens sometimes if you put in the effort (learning/memorizing/training). While I am not old enough to know how it changes, could it be perhaps that what you had learned when you were 16 was in your mind a certain pitch and as ears change (a 16 year old can hear higher pitch than 30 year old), you don’t relearn it, therefore it’s shifted? Please correct me (pretty sure I’m wrong)
I have it from early age, and it also shifts now that I'm almost 40. I think the more constantly I use it though, the more it seems to settle back into accuracy.
Thank you! That's really interesting. So it's like a muscle I guess. More you use it = better.
That's not true for everyone. Some extraordinary musicians with perfect pitch also reported that it starts drifting for them as they age (I remember Oscar Peterson and Jacob Collier telling this)