What's above senior? Senior++?
More seriously I think something that can happen with older folks is they might fall into working in a single place with a single set of tools for a very long time so when they transition to something different it may be hard to adjust. Not necessarily because “they are old” but because if they did one thing and only that thing for 15 years it’s hard to change.
Thus at BigCo, hiring senior devs of advanced age should make sense to do.
s/a staff engineer/architect.
sometimes it's just junior, regular and senior programmer