Ok I have been battling with Lilly's ears for a while now. I was almost without any hope, but thought I would keep trying for another week. I usually only leave the tape on for 4 days max, But I thought that if it didn't bother her I would leave it on for the entire week. Mind you Lilly is 6 months old and l@@K!! 
So, I would say that if you are persistent. you can make them satnd, even at 6 months old.. ANd as I'm sure you can see Lilly's ear are pretty big and heavy too!