Bradley served to August 1953. The story never said Downs was on Bradley's staff during the war.
It's very possible he was on Bradley's staff in the late '40s or early '50s.
I'm not saying Downs' claim is correct or true, I'm just saying that the claim he'd have only be 17 in 1944 is not relevant to the article.
From the article:..”the 90 year old Downs says...” That certainly implies that he is 90 now.