The Sep. 06 issue of "Professional Pilot" magazine says the following about one of their writters. (See page 12)
"Brent Holman began flying at age 12 and was fortunate enough to become a major airline captain at age 23. These days he's a Florida based senior check airman for a US-based major airline, where he has also held a variety of flightcrew and operations management positions."
I don't know what airplane he was Captain of at age 23, but at a major airline it does'nt get any younger than that.