Right, Caleb was 6 months old when we got him and he weighed 17.5 kg, he was easily the size of a labrador or golden retriever, he hasnt grown more than an inch or size height wise but he has put on about a kilo, i was just wondering what his approx adult weight will be and at what age he will be fully grown? hes obviously bigger than his collie parent already and aside from his colouring and texture of his hair he doesnt look particulary liker a collie, he looks (in shape anyway) like a flatcoated retriever or golden retriever, althoug having said that i am not convinced of his collie parentage but i am no expert!
At 6 months I would say he should still be growing, but it's really hard to estimate for mixed breeds. I wouldn't say more than 30kg, but obviously this is a long way off. If your worried he is putting on too much weight then have a feel of his ribs. You should be able to feel them, but they shouldn't be protruding or visible if he has a short coat. Hip bones are another good one to look at if they are underweight.
Mine is 22 kg now, when we got her from the rescue centre she weighed 30kg, and they said her target weight was 22-25kg. She is 9 years old. I would say her shape is more retriever than collie. I hope this helps.
It's very hard to say with first crosses - as owners of Labrador x poodles are finding out when their puppy grows taller and bigger than either parent! If the puppy tends towards the Retriever in looks, then look to the Retriever as to what to expect. They can be quite big heavy dogs if from show lines (working Retrievers are smaller and more slender with finer bone).