what shocks me more in term of inconsistencie is rather the fact that Oda is praising older people, that in his manga, the older you are, the more powerful and wise you are and that he is against nerfing older ones just because they are older, and yet killing for the sake of the scenario - at best because there is no other explanation -, the WSM, by saying that he was old'n'sick.
Oda is full of inconsistencies sometimes.