i have seen dogs as old as 6 get there ears clipped, just remember the older the dog the shorter the cut. a shape of cut all depends on the bell of the ear, a pit with a side flop, or colby style ear usually has a better stand because of the bell of the ear versus a front flop more common with AM STAFFS, and AM bulldogs and so forth.
im not an expert just what i have personaly seen and liked, i do not make a habit of clippen ears.
my lil blue dog shamus has the idea ear to me on a pit, cut or uncut!