Hi there, Twix, my chocolate lab, is 7 months old. I have been seeing other labs younger than him and MUCH taller and heavier. Is he just a small build or will he suddenly have a growth spurt? Nothing I can obviously do about this, but anyone else got a small pup, would be nice to hear from you! He is currently: 7 months old 20cm from floor to shoulders (it wasn't completely accurate, but not far off) Last weighed about a week ago and he is 16kg. The vet hasn't said anything, and said she is happy with his weight etc, but just makes me think "poor little thing" as he is so tiny! (Lovely for the house though as doesn't take up too much room! haha)
I had a huge lab a really tiny one and now and skinny middle sized one. My huge one was wonderful and my middle sized one is just a lovely sweet cuddle bunny, but the tiny one well shes the most fun and cheekiness packed into a tiny body. She is not even 20 cm at the shoulder and weighed about the same as your pup at that age.She was a tiny pup and stayed small but she thinks shes huge. As long as your pups healthy and your vet is happy its not a problem. he may grow a little more develop more muscle as he gets older, but i love my pocket sized lab. I would rather carry her home if she's injured than my 2 boys.
Agree with Everything @SwampDonkey said, there are advantages to being a bit smaller with lifting, etc, so as long as your vet says Twix is fine I wouldn't worry. Plus you might be due a growth spurt. Monty was well below average in size and weight until 5 months when he suddenly caught up and is now a tall leggy lab.
Yes I have a diddy girl too (although I wouldn't dare tell her so) - she's 19.5Kg at 5 years old and was about the same weight as yours at 7 months too - she's a feisty little girl - excellent gundog retriever - will go all day - wins scurries at the fairs as long as they don't involve too much high jumping - lovely little girl - rules the roost over my other bigger three labs.
My boy is quite small too - I haven't measured his height but he weighs about 35lb / 16 kg at 6 months and one week. He's an American/Field lab so he's more slender. But he's still rather petite and has petite paws.