I know this is an old thread, but I wanted to add my experience on this in hopes it helps anyone else. I'm a first time sheltie owner so my experience is very limited. The breeder glued her ears at 9 weeks for me and I tried to continue the practice afterwards. I found that she'd rip out her hair with little balding spots and sometimes minor bloody dots. The problem was within two weeks or less, I'd have to redo the process. I was running out of hair to glue and my option was tender bald spots to adhere glue to. So I gave up on gluing ear to fur in a very short time. I wasn't confident in the taping technique. I decided I'd be okay with prick ears.
Then within a couple of months, one ear just tipped on its own. The other stayed prick. My husband thought it made her unique and cute. I guess I just saw asymmetry and I just preferred it be either pricked or tipped, but not one of each! I let it go and then when she was about 1 year old, I decided to try weighting and gluing after I read it somewhere online. I purchased Torbot medical grade glue so it wouldn't irritate her skin. I bought tungsten powder. I mixed the combo in a little bowl and applied the weighted glue to the tip of her pricked ear with q-tip and shaped the weighted glue until the ear was set just right. I didn't think it'd work, but I've been doing this for 3 months and now it seems her ear is holding onto the tipping by itself! I'm going to keep at it, just to be sure. The nice thing about this is she can't rip it out so there is no hair loss, no balding, her skin isn't irritated by the medical grade glue and it lasts a few weeks in her ear so it much less effort.
I know there are different kinds of ears and each dog is different. I'd say my dog has thick ear leather and maybe I've been lucky it has held after the age of 1 year old. I will update this later if I find the results are continuing to hold (or not).