(Projoy) You can't learn absolute pitch, or unlearn it either, which is one reason I play the trombone. All the other blowing instruments in a jazz band are transposing and if I read a C I don't want to hear a Bb, and certainly not an Eb (alto and baritone sax). Trombone is written in bass clef, which results in an impressive stack of leger lines for the high notes. If it's on a space and "in the stratosphere" it's a C (octave above middle C). Otherwise it's a D (hopefully a Db) which I can just about do with a following wind. Why don't they just go into treble clef? Because they don't. Maybe not all trombonists are pianists.
To answer my own question re: perfect pitch, I googled a paper which says: "we also observed a significant association between AP and the age at which an individual first began playing music. For the AP group as a whole, the mean age of starting musical activities was 5.4 ± 2.8 years, whereas, for the non-AP group, the mean age was 7.9 ± 3.2 years (P < .0001)."
[Projoy] But -- as they also point out, I'm glad to see -- the causation could easily run the other way. [Bm, Raak, Darren, et al] This is a *great* discussion; one from which I am really learning.
I had perfect pitch as a child, but not being a musician, I've never used it, and the skill seems to have decayed. I just tried whistling a middle C, and it turned out to be a tone flat. But maybe I'm channelling Baroque pitch, concert pitch having been invented to boost the E-string industry.