Nope -- he was a prodigy from the earliest age. He was composing music at the age of 5.
Thats kindergarten. You might be thinking of other composers who are regarded as his equals -- Mozarts brain was just tuned for music in a way ours are not.
I would have been composing at 5 had my father been a musician/composer/teacher! (I did start piano at 4, in a not-particularly-musical household) As it was, I remember hearing that when I was about 9, and thought "Oh well, it's too late for me" - which is a shame! But his first compositions weren't great. You write that like it's some super-human feat or something.
"he was a prodigy from the earliest age. ... Mozarts brain was just tuned for music in a way ours are not." I don't know why people talk like that. Maybe as an excuse for not achieving great things themselves, or even having to try.
There was a Hungarian guy who decided to train his 3 daughters to be chess players, to see just how good they could be given a proper training. The 2nd strongest sister became world champion. The strongest one never played in women-only events, she was too strong, and turned out to be the strongest woman chess player of all time, by a long way. (i.e. Susan and Judit Polgar) I don't think it was because their brains were 'tuned for it'. They just had the perfect environment.
Another example, this[1] music producer's kid developed perfect pitch despite the lack of any training. He was exposed to a rich variety of complex music right from the start. When the dad discovered his son's ability, he found out that the kid had his own names for the notes. IIRC, based on which song begins with that note. I think it's quite likely that if the dad had spent all his days composing music, the son would have been doing that from an early age as well.
Your proposal can't actually test the hypothesis because it can't (reasonably) be done. We don't know how many children were similarly situated and did not turn out like Mozart.
It could be that many musicians with a similar background were/are similarly as good as Mozart, and Mozart's music is especially famous for its cultural appeal and his father's aggressive "marketing" to royalty. There are many reasons one particular musician's musicical legacy can succeed aside from raw skill and creativity, much like the success of a company has a nontrivial luck component.
It could also be that he really was extraordinary above and beyond his family's musical background. Like most discussions about the nature versus nurture of genius, we can't really assert one thing or another.
Is music composition difficult? Are most five-year-olds asked or encouraged to write music? Is this something that most adults have attempted and failed to do? Do you think that you could write a piece of music if you had time and inclination?
I'm asking honestly, because I'm pretty sure that I'm not having a typical life experience. Personally, I don't really bother to listen to music, because music is never further away than wanting to hear a melody. It's something to do on the bus, or when my mind is otherwise unoccupied. One starts with a note or a scale, finds a 'lick' in it, develops it into a theme or refrain, introduces a counterpoint or noodles around through the keys a bit, and eventually we work around to a restatement or finale (or get bored or forgetful in the middle). I suspect that this is easier for me than others, but I don't think that I'm any kind of musical genius. I'm at least hoping that creating music is more of a normal part of the human condition than not, at any rate.
