How far is to far?

Question
I have a 5 month old GSD, he is 60 pds.  We are walking 1 mile in the AM and 1 in the evening.  We get about half way on our walk and he lays down.  Front paws spread out and head glued to the ground.  Am I walking him to far?  He sleeps all night and most of the day.  He has obediance training and does fine and minds most of the time.  Should I continue to force him to finish our walk or let him say I'm tired and take him back home?

Answer
That doesn't sound like it is too far, but is is best not to push a dog too far until it is a year or 2 old.  Give its joints more time to develop.  For the same reason, switch to an adult chow now to slow growth.  That reduces the chances of joint problems after it reaches its full size.