Why the arbitrary age 56 cutoff?
Unlike a lot of folks here, I think the main job of a veep is to take over leadership of the party once the POTUS can no longer run. Hence, I think it's important not to pick anybody who's too old to reliably run two presidential campaigns. To be fair, though, I could probably push that age limit back to 60.
Disagree. The main job of the Vice President is to be able to take over the presidency at a moments notice. Political considerations are secondary. I am not against a younger VP, lord knows we need younger leadership in this country, but an arbitrary cutoff line excludes many people who would be very good at the job.
The real job of the Vice President is to do nothing until called for, which can be very boring, unless the President is of reduced mental capacity.
The No2 spot on the Ticket has more fun and responsibility in an election campaign.
That's why they are mainly chosen on campaign considerations, not heir's apparent.