I didn't say anyone can become Michelangelo. I said anyone can do this level of work.
That is, the exact same thing he did when he was 12, which is a master study. He didn't create the design - he copied a previous work and added color to find out what Schongauer's thought process was when making the original piece.
I very much doubt the majority of adults with sufficient practice could do this level of work. I can say with 100% certainty that an infinitesimal minority of 12 year olds with sufficient practice could do this level of work.