[LunarBerry]

I remember having a similar question to this but it was for when to switch to dry and my furbaby pretty much decided that on her own whether I liked it or not, lol (snubbing wet food and going after the dry "big" girls food)
I started to integrate adult food (mixing with puppy food) for her when she was around 9-10 months, but it was a large mix so we wound up having a adult/puppy mix waaay past her full transition for adult feeding. So at the beginning of summer (a couple of months after our birthday), we gave that mix away and switched over completely to an adult formula for small breeds. So I'd say at least by 1 years of age, give or take a few months, but transition a little before that.