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I joined BA in my late twenties on a wide body. At the time there were skippers on the fleet that had been given their commands at 30ish. In my six years in the carrier we have hired directly on every fleet in the airline including the 747/777.
New hires come from three back grounds. These are cadets, direct entry experienced and of course the military. The cadets can be as young as 20 and after a five years on the 320/737 they are free to move to other fleets. Some of the direct entry pilots may very well have the hours to go directly to long haul as well. This might explain why you are seeing younger looking FOs state side.
Seniority at BA is as important as it is in North America for many things but our pay structure is set up such that time in BA not aircraft type determines income (to a large degree for FOs) as a rule. Status pay to be precise. That being said ask a very young looking BA long haul FO the last Saturday night they had at home and you might get a blank look!
Hope that helps.
