I think it's an interesting discussion.
I have heard people state that people can always be taught to sing in tune and there's no such thing.
However my dsis is tone deaf. She's very aware and has tried lots of different ways of learning. She can just about follow a tune if it isn't too high/low and she knows it very well. But she doesn't sound natural, perhaps like watching someone act who has learnt exactly where to stand, how to position their body, do the voice inflections, but somehow it isn't natural.
My borther is also tone deaf, but doesn't realise. He'll swear he's singing in tune.
I started singing in tune at about age 10, but I had to concentrate very hard. I can hold a tune now, and have quite a big range, but I can't harmonise, I can't sing against another tune.
Dh has perfect pitch-give him a chord and he'll tell you exactly which notes are played. He couldn't sing in tune until he was about 10/11. He now has quite a nice voice, and can harmonise and sight sing without any difficulty.
My girls have singing lessons. Dd1 was singing in tune from before she could talk. She's got a nice voice, I suspect she has perfect pitch, she can harmonise etc. very easily.
Dd2 is much more like me. She didn't really sing in tune until she was 7 or so. She now still will lose pitch if she isn't concentrating, but her voice is improving, and she has a lovely tone when the range is right. It is possible she will end up with a nicer voice than dd1.