Hi! My apologies for the while it took for me to reply - I was about 70% sure I'd seen an elder version of it somewhere, but my memory was being particularly hazy and I'm wondering now if I was just imagining it. Hmm.
I enabled it for elders for you (download here and let it overwrite the old files). It uses the adult mesh, because I'm personally not sure how visible an actual mesh conversion would be with the shape this particular robe (elders have slightly thinner arms and a thicker waist). I hope that was what you wanted. :D
Enjoy!