Join Date: Mar 2016
Location: Ontario, Canada
By vest you mean backpack / harness correct?
I would weight until full grown for a backpack that has weight to it, you can start with harnesses (without bags, just a regular harness) from the day you get her basically to make sure she is comfortable with the feeling of having something like that on her. then at about a year and a half, have a empty backpack on, maybe with poo bags or a ball on each side, very lightweight, nothing crazy to get used to the backpack feel, then after a few months, closer to her 2nd birthday i would start putting weight in it like heavier things, water bottles etc..
Thats about the timeline i would do for backpacks, other people might have different answers