Hi your Prince Toby is adorable. I got my puppie last year at about 13 weeks old and she was the smallest of the litter. She only weighed in at about a pound when she was 8 weeks. I'd say she has put on a bit of weight since we got her and probably doubled in size. Looking back at the video of her when we first got her she has come on leaps and bounds. She was the smallest of the litter but the one that showed all the others who was boss and had a lovely personality about her. She is a very loving dog.
I hope you have as much enjoyment out of your puppie as we are having with ours.
Sometimes you can go off the size of the paws if they are going to be a big dog or not. Hope this helps
Best wishes
Susan and Fenway
xx