Great Video!!!! Great Dog!!!
About growth plates... in horses we had to wait for them to turn 2 years old before they could be expected to carry any weight for an extended length of time, and/or do a gentle gallop...not to be pushed to run hard due to concussion injuries to the legs. So I researched a bit for dogs ... site wouldn't allow cut and paste so here's the link:
Growth Plates
Basically says to xray to be sure, spayed females may take longer for their plates to close due to the early change in hormone levels, and jump training would be only over something on the ground... no height until the growth plates are definitely closed...
I think playing in the snow or anywhere is fine, just don't push them to perform or run or jump to their limit, or allow them to play too hard or to weakness/exhaustion. A good topic to discuss with your vet...as he/she would be more familiar with the conditions where you live and what dogs can be expected to do in those conditions, and what to be aware of and watch out for. (or your agility trainer)(or both)
