These 90/100% figures really vary by society. I'd argue that in Ireland, because of the public singing culture, there's more people that can sing passably than in the US. Like learning another language, you're much better off doing it young. I know many fellow Americans who never sing (and are embarrassed to, even though no one has any great expectations) and as a result aren't even passable at it. Relative pitch recognition and vocal pitch reproduction are both nontrivial and better learned young. Fortunately I had some music classes in elementary school that involved singing and I've been singing along to music ever since and thus am OK at it, but many people haven't and aren't.