I would say the average age is early twenties. After mam and dad have paid for the training and type rating, they go straight into the right seat of a modern jet. Where i work it is not uncomon to see captains in their mid twenties. these guys and gals can expect 40 years of jet command time, and salary.
Absolutely not the case in the U.S.
Most folks at my company were hired in their mid-thirties to mid-forties.
Those hired within the last 8 years or so are looking at 12 years minimum to any left seat.
For the last ~250 pilots or so, they can expect 10 years just to get off the 727 panel.