Some marvelous video of Lefty Grove, possibly the best southpaw pitcher of all time:

Those mechanics are a thing of beauty...smooth as silk, no wasted motion, no awkwardness.

He was trapped in the minors until age 24 because the Baltimore Orioles of the International League refused to sell his contract to a major league club. He won 300 games anyway. Nowadays, someone like this would likely have been in the majors by age 20 or 21.