Your son as a nominee can travel without you either using your yearly firm concession or on standbys but in both cases his priority is greatly reduced. If he uses your firm concession he wont have the same space available upgrade priveledge. Just discovered that by creating a dummy booking.
Standby flights are not as attractive as they appear. They are quite expensive, often the lowest class commercial fare (if available) is cheaper than a standby ticket. The only benefit is they are fully flexible and refundable. But that doesn't help when you have a hotel booking that you can't get to or cancel.
You should be able to look at the facts on the retired staff site.