I don't think there's a set trend, because sometimes a 33 year old won't drop at all, and some guys will only drop once or twice at 34 (i know a example of this in a former player i had Diego Armando callejas).
no career extension coach, but he never dropped, i sold him and i saw him being sold later on his skills were virtually the same (he actually popped as a 33 year old and a 34 year old lol).
so i think it's random for different players.