My chocolate lab just turned 6 months old and weighs 70 pounds. He is already bigger than my roommates full grown lab. His parents were big but how big do you think he is going to get? He is not over weight but he still has some puppy fat.
how big were his parents? the breeder is the best person to ask how big a dog will get and a vet is the best person to helps on "healthy weight". generally you want to easily feel the ribs without pushing in. if you can't - he needs to loose weight.
labs are one of the most overbred breed. people randomly breed them to look all kinda of shapes and sized.
so it is very hard to compare what your lab will look to what your roomates lab looks like as it depends where you got your labs.
You cannot compare lab to lab. Depending on the pedigree etc. you may just have a lab that matures quickly. You can't compare an English lab to an American lab.