Please have a look at the links for further information on canicrossing, bikejoring or skijoring.
These can be done by all ages of human – depending on ability as regards to biking/ skiing – but if you’re very young then an adult needs to be attached to the dog as well.
Also for competition no-one under the age of 7 would be able to run as again just a little too young (sorry!), and 7-10 you need to have an adult run with you who is also attached to the dog.
Dogs under the age of 12 months are not allowed to run competitively in any sport, as it might damage the proper growth of muscles/ ligaments/ bones. However at 12 months they can start to compete in canicrossing, and at 18 months bikejoring.
They can be introduced to the sport of canicrossing earlier but just in short sessions, it is quite a good way to teach them commands (including to ignore another dog(s)) and also to socialise with other dogs and humans.