Length of dog walks for our 6 month Lab Pup

Question
Hiya, weve just recently bought a 6month old female lab from a breeder. We have been taking her on walks sometimes up to 2/3 hrs, we are a bit worried as someone has said we are walking her too much and will damage her legs. She enjoys her walks, she is tired at the end but is quite happy. I cant find any guidelines online regarding the sort of mileage a lab pup of this age is recomended to walk a day. If you could help me with this it would be greatly appreciated. Many thanks

Answer
Many of the guidelines you do find are more guess work than science.  So many people assume whatever they have always done is the right thing to do.  I don't remember seeing any guidelines on this from a source I would trust.  I do know too much running and jumping is bad at that age, and you should never push a lagging puppy.  We have had 17 puppies that after a year old passed the rigorous physical including hip X-Rays to be a dog guide.  Many of them we took on long walks even as 7 week olds, although when they got tired, we picked them up and carried them.  As long as you aren't setting a fast pace on pavement, my guess is that you aren't hurting a thing.  Others might not admit they are guessing.

The 3 hour walk is a staple for professional dog trainers.  If they have no other answer, they suggest that.  I don't know they limit it to adults.  

What I do know is that you need to keep the puppy lean and avoid fast growth.  Switching to an adult chow for the larger breeds at 4 months, slows growth and helps develop sturdier joints.  Be a little careful.  some adult chows have over 1.5 % calcium, too much for a puppy.

Your dog definitely should be narrower at the waist than the hips and chest. You should be able to easily feel the ribs, but not see them. Each dog is different. Standard recommendations are a good place to start, but each dog must have its food and exercise adjusted to its individual needs. Here is a link to a good illustrated guide, http://www.longliveyourdog.com/twoplus/RateYourDog.aspx