Most of us with puppies will have seen the advice stating that you should not walk a puppy out for more than 5 minutes per month of its life (i.e. 1 month old walk time = 5mins; 4 month old walk time = 20 minutes) To me this seems like a fairly good guidline BUT I think it should be taken with a pinch of salt after all how can you prescribe this same amount to every dog regardless of breed, size etc.
Sometimes if the weathers nice I like to take my pup a bit further than this (depending on how much energy he seems to have) and the other day I took my 3 and a half month old for 2 x 15 minute walks (amounting to less than 1.5 km distance in total for both) in one day. When this came up in discussion with a friend, who also owns dogs, they said they thought that this was risky and that I should stick rigidly to the advice or risk my dogs health.
I think they are being a bit too precautionary as I have never know of any problems caused by this, but I value this friend's opinion so I thought I would put it to the forum and see what you guys think.