Calendar vs cycle aging
A battery ages on two clocks at once: time (running even while the car sits) and use (the charge cycles). The two add up.
Two clocks are ticking. The calendar clock advances just with the passing of time, even if the car sleeps in the garage: the chemistry degrades slowly no matter what. The cycle clock advances with use, as you charge and discharge.
What speeds the calendar clock is keeping it at 100% for long stretches and, above all, heat — key in tropical climates. The cycle clock depends on the total energy you've put through it. So a barely-used but old car, or a new but heavily-driven one, can reach a similar SoH by different roads.