My other dogs were before the internet. I do remember the 864 comments I received about how big their feet were and that they were going to be 100 lb dogs (the biggest was 68 lbs and he never grew into his feet).
Sam was a rolly-polly puppy. I got him at 10 weeks and 30 lbs. He was 52 lbs at 16 weeks. He got up to 110 lbs, which was too heavy, so I took him down to about 80 lbs. He holds his obesity well and no one guessed he had 30 lbs to lose. He's about 85 lbs now as he has gained some muscle this summer from all of the swimming. He definitely was not full grown at a year old.
Linus was about 45 lbs at 16 weeks. He topped out at 96 lbs when he was a little over a year old. Field people thought he was chunky but the vet thought he was fine. I took weight off of him because of the jumps and the field work. He's about 80 lbs now, bigger boned than Sam and naturally more muscular. Linus was an early bloomer and doesn't look too much different between a year old and now (three).
I do keep them lean with a back rib or two visible in the right light (hard to see under all that coat). It helps with their endurance, energy, jumping, ability to work in the heat and in their future health. I can't believe the difference! Just because they are conformation bred doesn't mean they need to look "ring ready"! The double the weight thing has been a rule of thumb for us, not science. I think it can help people keep things in perspective. I know a lot of people who thought their dogs were going to be huge because of feet or the size of the dad and then went out and bought giant beds and collars, only to end up with a 45 lb dog.
It'll be interesting to see where Brooks ends up on the scale. How tall do you expect him to be? My boys are both 24".