Its all down to luck to be honest! These young types that get on the heavies at such a young age have the contacts! Daddy flies for x airline and hey presto your in through the back door!
Most of them dont know thier arse from thier elbow but they have the contacts/connections!
I think that's incredibly unfair.
If you start training having left school at 18, finish 19/20, you could be in the right hand seat at 20/21 if you were lucky with the timing and airlines were hiring. Say you were flying for 3 odd years for any short haul airline and you applied to BA, they could offer you long haul as you would have >2000 hours. So it is plausable to be flying long haul by mid-twenties. Yes, it's all about luck, but it's unfair to say every young pilot is crap and only there because dad's the chief pilot.