At six years old i would say he has a bit to go yet mate,however if your doing a lot of work with him,and he is getting that bit older he might need longer time of between digs,make sure he is fully recovered from previous dig before working him again,dont work him sore or you could risk putting him of his game altogeter.Give him some time off,and pleanty of road work,he'll soon be keen to go again,know your dog and his capabilities.I have a 12 year old patterdale dog here at the moment who has seen a lot of work over the years and still has the ocasional dig.Heres a pic of him about 4 or 5 we