Wow, your girls are robust little ladies - they are as big as Truman, who is a little older than they are and a male. He weighs 46 pounds (as of Tuesday) and is in good shape, though I know he has much more growing to do. I suspect he will top out around 55-60 pounds like Bentley. As [MENTION=2]desertskybulldogs[/MENTION] said, I would keep an eye on their weight because, take it from Linus, it is hard to get that weight off once it goes on!
My bullies never got to full size until they were about 18 months old. They kept growing and changing until that point, when they really filled out in the head and chest.
As far as heat goes, I believe the females go into heat at about 6-9 months. Are you planning on getting the girls spayed yet?