I'm a military kid, both parents in the military - Mom did 12 years, Dad did 21, served in two wars. So discipline is something that was huge.
I think there are so many ways to become interested in music. I believe signs of sustained interest gives a sense of the right time. Music, if thought of as a language, would perhaps indicate that as early as possible is not so bad. I do believe that a really nurturing first teacher that makes the child love something is crucial.
I haven't any right to criticize books, and I don't do it except when I hate them. I often want to criticize Jane Austen, but her books madden me so that I can't conceal my frenzy from the reader; and therefore I have to stop every time I begin. Every time I read Pride and Prejudice I want to dig her up and beat her over the skull with her own shin-bone.