Retaining Wall Restoration
Not age so much as settling in the footing. You'd see the same thing in a new wall in similar circumstances.
You have two options:

Replace the entire wall section, say 15 feet out from the corner both ways, including the footing, to try and be sure that it won't move further. You'll examine the soil under the current footing and possibly improve it, making sure to compact thoroughly. This is obviously a substantial job and would take several days.

Remove and repair just the broken block, hoping that all settling that will occur has occurred, and that the footings are in their final resting place, so to speak. A good mason or bricklayer can do that job in a few hours. A mortar hack like me would take the wall apart such that it's a stair-step all the way up  (to avoid tuck-pointing) and might take a day.