Hi, both the argument in D and the initial argument are about absolutes. We have one variable, height or age, that determines another variable across all cases.
A is slightly different. A sets up a universal rule, which is the same, but the rule only compares individuals to their past selves, not to other people. We know that we get wiser as we get older, but it fails to account for possible variations in wisdom between people. It's quite possible that the younger Persian was a born genius, and that the older is an absolute idiot. While the older is wiser than they were when they were young, they might still be an idiot, just slightly less of an idiot.
