seat 0A - The jobs of Commander and F/O are different and require different skills. I am glad you 'feel comfortable ... knowing the aircraft is in their capable hands' and so you should. Baring what should be more experience in the left seat there is no reason why the F/O should not be equally as good at handling the aircraft as the Captain. And, when you are tucked up in the bunk should something go wrong the F/O is there to cope admirably until you arrive to take control of the 'situation' and make the important decisions from then on; something the F/O is not yet licensed to do. Experience, training, qualifications, promotion and personality will eventually qualify them to be in your position. I concur with cavortingcheetah's view and feel that age and life experience do play a major part in preparing a F/O for command.
Three other points:
in my experience passengers generally have more confidence if the captain is a 'little more mature';
the older you get the less you have to prove and therefore the less 'ego' there is in the flight deck which generally makes for a more pleasant environment;
being the captain is not what everyone aspires to and there are many excellent F/O's who do not want / will not make captain but are just as much support and value in their operation as anyone else.
Personally I feel 65 is old enough to be in command of a commercial airliner.
Using your experience in the sim beyond that age may well benefit the next generation providing you don't lag behind as procedures and ideas move on.