I have a couple of friends that were hired at an airline (commuter/regional) at the age of 19 in the early 80's in America. So they could easily have 10000 hours by age 30. That is not so likely today as most airlines require the ATP license now before hiring. Our rules say you must be at least 23 to apply for an ATP, and 1000 hours is the maximum you may fly in commercial airline service in any calendar year. Employment history combined with the logbook totals would be a fairly reliable indicator of a candidates experience. You could pretty easily falsify several hundred hours, but thousands would be easy to spot.