This area sits in a cold-climate band with severe winter exposure, and steel panels take that differently depending on how old the coating and gauge are. On doors from the mid-1950s, decades of freeze-thaw cycling on original paint and steel tends to show up as rust-through at the bottom panel first - that's the section closest to road salt spray and standing water, and it's usually thinner-gauge steel than what's used on newer doors.
Dents matter too, but on stock this age, rust does more of the damage over time than any one impact. If you're noticing flaking paint with soft spots underneath rather than a clean dent, that's the panel telling you it's been going for a while, not something that happened last week.