R attacks S on the grounds that S is too old. S does not dispute the allegation, but rather act like they are taking the high road, while bringing up a separate age related issue; that R is too young.
R does not show that S contradicted themself. While R may show that S' line of reasoning exposes a flaw in their own campaign, this is different from saying that the argument is self contradictory. This would require that premises actually contradict each other, or the conclusion. This is not what we see here.
However, S does not actually respond to R's claim. Rather, S draws attention to a different claim related to age. He never disputes the fact that he may be too old for office.
