One factor which has not been stated is that in the case of this a/c fit in the incident in question the a/c can only be taxied from the LH seat.
If you are arguing that "younger and sharper" pilots are more acute at picking things up then perhaps it would be safer if they were able to taxy the a/c from the RH seat and then put the Captain in a monitoring role, rather like a monitored approach.
Of course experience does not mean you never make mistakes and in a well crewed flight deck errors should be picked up by PM but it does enable you to see the wood for the trees in many situations as you've probably been there before and even, dare I say it, had the odd near miss but lived to tell the tale.
In my experience a lot depends on the individual. I have flown with experienced pilots in their 60s who are easily on top of their game and the odd one who isn't. I have also flown with newbies who are likewise.