Fast growth - too fast?

Question
Alright, it is kind of ironic that I am now concerned that my Oldie puppy may be growing too fast since last month I asked you how to get my puppy to eat more.  I am now free feeding her and she eats throughout the day consuming about 2-2.5 cups of Iams Smart Puppy.  She is now 14 weeks old and weighs 21 lbs.  She has been averaging about 2 lbs of weight gain per week for the past two or three weeks.  I've heard other nonbull-breed experts say that growing too fast can cause joint problems.  Is this true of Oldies (or regular bulldogs for anyone else out there wondering)?  She is somewhere around 12 to 14" at the shoulders (it is hard to measure because she squirms too much and wants to attack the tape measure) and I figure most of the weight she gains is going to thickness, not height, since she will probably only be 3 or 4 inches taller when full grown anyway.  You can tell by looking at her that much of the weight that she is gaining is going to muscle - her muscle tone is really developing nicely and I can still see her ribs pretty easily, so she isn't getting fat.  What do you think, should I try to slow her down a little, or do you think she is ok at this rate of growth?  She was the runt of the litter, and when I first got her, I expected her to end up at about 60 lbs.  Her mother was 65 lbs and her father was 80 lbs.  Now I'm thinking she will easily weigh the same as her mother and maybe a little more (which is fine with me - I picked her for her wonderful personality, not because I was hoping for a smaller dog).

Answer
If she's not fat and she's developing muscle, then she's fine. The weight is going to the right places as it should. The amount she's eating isn't much at all for a growing puppy. 21 lbs. at her age isn't too much at all. You're doing fine. Don't change a thing.