It can be dormant in adults. I discovered it when I was 16 after meeting a pianist who had it and “taught me” how to do it. I kept getting faster and more accurate as I practiced solfeggio in music school in my 20s.

Crazy thing is it changes with age. At around 30 I started regressing. These days I identify the tones but shifted by one semitone.

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)