young dogs and exercise

Personally, my Collie pups can easily walk a mile by 4 mos of age.  I don't do too much with them until at least that age.  You are right, though, every dog is different so I can't speak for other breeds.

I think there are varying opinions on this.  Personally, I let Ben run until he's tired, as long as it is on grass (or occasionally, very spongy earth on the path through the woods).  He's 4 1/2 months and a Lab, and frankly, if I didn't let him run, and run, and run, he'd be unmanageable in the house.  The days when he doesn't get as much exercise are definitely noticeable - he won't sit still and zooms around the house, picking up tennis balls and tossing them at me.  I don't walk him AT ALL on concrete though, unless I absolutely have to. 
 
We recently got lost on a walk and wound up walking for about 2 hours, much longer than we'd been planning to.  Ben had a half hour swim in the middle of it, and still did the last 10 minutes of the walk at a flat out run. 
 
I am careful about Ben's joints, and I give him a joint supplement, but he needs exercise.  I think that's true for all breeds, but especially high-energy ones.  Playing "hide" games in the house helps to tire out his brain, and that DOES make him tired, but it really only goes so far. The only "rules" I'd advise are no jogging, walk on soft surfaces as much as possible, and let the pup dictate his/her own speed.
 
Kate

This is what I do, and yes, at four months my gsds can do a mile easily. 
 
I let THEM set the pace within reason.  I'm not willing to have to run to keep up with them, but if they start to dilly dally, we'll take a breather.  Our Mr. Ears was quite small and with him, I'd pick him up if he started to slow down.  If he was tired, he'd snuggle right on in, if not, he'd squirm and I'd let him back down.  Now, he (in hindsite) had some health issues, so that was exactly the way to handle things with him.
 
If you have a smaller pup, one that you can comfortably carry for a bit, that might be the way to go.
 
 

I think Glenda's got it right. My understanding is that it's not the exercising that should be avoided, just the regiment style walking or running that doesn't give the puppy a chance to take a break when it needs one. Does that sound right?

I started walking Diego just over a mile at 4 months. He's an apartment dog and needed to get out his energy. I turn around sooner if he seemed tired on some days. If I didn't do this he'd have puppy zoomies...cute as they are...I felt bad if he he wasn't getting exercised. I didn't walk him every single day either. Even now I'll take a day off if he had a couple of very active days. He's only 9 months and I'm concerned about his health, as any mom would be.
 
Luckily we will all be moving to a house in a few months. Same one Casey grew up in...my parents house. So they'll have a yard, geese to chase, and a big house. I'm very excited about this []
 
This exercise topic alway boggled my mind. [8|]

yeah, it's "forcing" the pup to stay in the same gait for prolonged periods of time, particularly on hard surfaces, or "drilling" the pup and the like. The pup exercised in such a way probably will appear to be fine, but he's likely to develop arthritis at a young age.
OK: human walking briskly for five miles, puppy allowed to move at his own preferred pace on a long line (most likely a full-out gallop interspersed with halts to sniff).
BAD: human walking briskly for five miles forcing pup to trot or walk steadily in the same gait on leash the entire time.

ORIGINAL: mudpuppy

OK: human walking briskly for five miles, puppy allowed to move at his own preferred pace on a long line (most likely a full-out gallop interspersed with halts to sniff).
BAD: human walking briskly for five miles forcing pup to trot or walk steadily in the same gait on leash the entire time.

 
Hmmm...I find this interesting. So it's OK to go 5 miles at your pups pace? If I'm running then Diego wants to be right underneath me. I've been teaching him "grass" means run on the grass. And I walk as soon as he slows down. I can't use a long line because of traffic. At least not on my morning walks.
 
Honestly, if I went 5 miles in Diego's pace we'd be outside for HOURS...he's sniff every bush and chew every leaf and dilly dally and race after his doggy friends to play. I run to encourage him a long so we're not outside all morning..and so he's exercising and get's a bit tired out for his day.