When we got Henry he was 16 weeks old as the breeder had kept him back as he was the runt of the litter and she wanted to make sure he had developed properly. His mum had a litter of 10, 8 were of normal size but Henry and his brother were only 5 oz at birth and had to be hand reared, sadly his brother died but Henry was a little scrapper and thrived. He is of normal size now but I don't know how long it took him to catch up. On the reverse with Syd and Harry they come from a litter of 8 all normal weights but as tots Syd and Harry were two of the biggest pups in the litter, yet now Syd is fine boned and petite and Harry is solid and chunky so it shows that birth weight and size don't always reflect the adult dog you end up with.