13 is great, very few decent breeders let their pups go sooner than 8 weeks and 13 will be fine. They will be a bit more mature and more attentive to you and to being trained, i.e. you will or should have more of their attention. We got our crew at 8 months so no way they are too old. Once they learn that you are their forever friend shelties give trust like few other breeds. You have to earn it but when they give it you you have something very precious.. Good luck on your journey let the fun begin and get ready to be trained... the big question will be who is boss here!!!