Does anyone have any information / website links to read up on exercise levels while pups are still young? They are large breed gundogs and I want to be able to advise new owners. 

The KC advice 5 minutes per month of life, twice a day.
http://www.thekennelclub.org.uk/item/395

Hi.

We have a 6 month golden retriever and we have followed the 5 minute per month twice a day, with a a mixture of on and off lead but not serious running just going at her own pace. Also watch her play with other dogs and don't let her get jumped upon or worn out by any bigger or rougher playing dogs.

Hope this helps.