My anecdotal issue is I did use Taste of the Wild for a year or so before switching to Victors but not long after my male dog developed all sorts of issue, yet

My anecdotal issue is I did use Taste of the Wild for a year or so before switching to Victors but not long after my male dog developed all sorts of issue, yet can I truly attribute them to the food or his age (14?). However from the article I cannot figure out, how long after the diet was changed before symptoms were noticed?