Are you looking for facts that will contradict your opinion?

Justin Bieber clearly was that. His youtube videos got him discovered at age 13-14.

Vanessa Paradis made her first public appearance as a singer at age 7.

There are several children prodigies I've seen on YouTube (singers, drummers, guitarists). They clearly have such talent that even at young age they do music better than most people would do with infinite amount of practice.

As to your question, the prodigy is, by definition, extremely rare. They clearly exist (Bieber, Paradis) but, by definition, you can't expect to have a lot of them.

And "why aren't 7 year olds headlining for Taylor Swift" is not a fair bar.

There are reasons 7 year olds don't do world wide tours that have to do with things other than musical talent. Like being in school or not being allowed to take a bus by themselves.