Safe or right age to start training with bicycle in endurance?

[yukidomari]

I was always told that large breed puppies should not have strenuous exercise until they are grown up and their bones have matured. Including dogs that compete in agility, because a lot of running or jumping with young joints could cause damage.

I am wondering what is the right age to start bicycling with Vlcaks. I would like to train with our Vlcak, but obviously not too soon if it might harm him.

What are people's thoughts about this? It seems like walking is not enough for him anymore and the park is not always an option.