I've read this thread with interest, as at 10 wks, i had the same questions regarding my german shepherd pup Bernie. He's now 19 weeks too.
I think common sense. At 19 weeks, ANY owner should recognise a tired dog. Its the one sat/led down. Not rocket science.
The "5 minutes per week of age" algorithm...
Clearly, they were not talking about my dog.
Here's a sure fire way to know how much physical exercise.
Take you dog on a special walk. For an assessment. Allow the dog to run off lead, time how long it takes to tire him. That's how long.
Off lead exercise, and your dog wont be forced to run around, it chooses.
Generally speaking, regardless of breed, any off lead run consists of the following pattern:
Run around like mad, kicking up your heals for the pure fun and freedom.
sniff around, and see what you can tell by the sights and smells.
Follow the interesting ones.
come see what owner is up to in that bag of theirs.
At 19 weeks, my dog is working.
he can train for about 5 minutes. That is when his concentration goes.
he can run around with his park mates for 15 minutes full pelt, then is knackered for 5. Then off for the sniff part of exercise.
Then ruled by his tummy, he'll come see what im doing.
However, at my leisurely pace, he can walk 5k's into town. No problems. Not panting, not sitting down to indicate he's tired.
Just like you, he can walk for a LOT longer than he can run. Its not rocket science really.
And just to mention on another point. Parvovirus. Not a problem if you have your dog vaccinated.
And vaccinated is what most dogs are required to be, to join a training club, enter a boarding kennel. etc.
Your 19 week old dog, is not so well covered by immunity from the mother.
But seriously read up on vaccinations, there are some new schools of thought, that its not necessary. In the end, read up, and YOU decide.
None of my children or i, have ever been vaccinated. For anything. We use homeopathic medicine. We have never received anti-biotics, ever, we have an immune system that rocks! because of it.
However, for my dogs, i vaccinate. As my dogs, socialise in much more 'intimate' ways shall we say, than my family of humans do. They exchange bodily fluids frequently. And socialise is something they must do, as i dont have places i go, where my dogs cannot come. Even work when they are well behaved enough and can be idle for 2-3 hrs at at time.
Kelpie x. I fostered a kelpie cross rottweiller for a while. Took her on a bush walk, she ran all the way, back and forth, rounded every other dog up- all day long! And when i got back, and collapsed, she napped for 1/2 hr, and still expected her walk at dusk, grrrrrr.
Kelpie - aka, four legged dog on amphetamines.