Average size for a bc?

My one boy weights 15-20 pounds more then the other. Spanky is pretty small. I think he is 25 pounds. Bandit is more like 35ish or maybe even 40. Is Spanky just oddly small?

Taken from the Dog Breed Info standered for a Border Collie

Border Collies vary greatly in size. My boy weighs 38lbs, my friend's BC weighs 21. I talk to someone online who has one that weighs 60.

Are these two the same age?

Yupp. They're brothers. Spanky was the runt though so I am assuming thats why he is so small. Everyone thinks he's a little girl. Might have something to do with he often wears a hot pink bandana.