[jedimastert]

> I find it dubious that you can only learn this by age 7 - although I'm sure it's easier if you're younger. Is there science behind this claim?

A better way to put this would be "difficulty goes up exponentially, much in the same way as learning a new language".

> I am not a musician, but I have recently started learning to play piano, and training my ear is something I'd really like to learn. I've used some apps to practice ear training, and I'm able to discern intervals decently, but I can't recognize and identify a single note on its own. I do hope I can get there with more deliberate practice.

As a professional musician, absolute pitch is very helpful but definitely not necessary. Being able to hear intervals and the contours of a melody well enough to pick it out quickly (this also goes for recognizing what kind of modes scales are being used, i.e. major, minor, penatonic, mixolydian) is so helpful that I might actually call it necessary, depending on what you plan to do with your music.