It's probably agility as well coupled with the heat/humidity.
Personally, I do a lot of walking around, much more then when I lived in the Usa. I guess he could drive everywhere in his truck, but somehow it seems harder to do here. You start getting tired and winded when you get older.
Add on some sweaty hot weather, walking on shoulders with traffic and no sidewalks, and it's probably unbearable being really overweight and older. I wonder if he needed a/c a lot? Maybe one of those guys who sits inside with a/c all the time.