Klimt did the first three when he was 17. There are even earlier works which are not much less sophisticated.

http://art-klimt.com/early_works.html

Some people are just prodigies - very, very few, but it's a real phenomenon. Even with early craft training, which people don't get today, exceptional talent still cuts through.

This is why the common "There's no such thing as talent, it's just hard work" line can't possibly be true. It's soothing to believe that you too could be a genius if only you put the hours in, but it just doesn't work like that.

Ability is set by a talent ceiling, which is on a bell curve. "Most people don't reach their ceiling" and "There are extreme outliers of native ability" can both be true at the same time.