Here in Mexico we have Pepe Messer who started flying LearJets when he was 17, he was captain of every Lear in the 20, 30 series by 19, then he went to the airlines, and by 23 he was 757 Captain, by 25 became 757 crew team chief and gave instruction at Boeing.
It is not uncommon for 19 or 20 y.o. to go into heavy jets with 190 hrs and a brand new license here in mexico. The neat thing is that there seems to be no effect on safety since we have a pretty good safety record over here given the conditions.