i have a 11.5month old whippet he gets a hour walk a day maybe more. some say 5mins per month of age but tbh i agree its load of crap. how can u regulate a puppy running around, jumping on couches and off and generally just rallying around the place? im sure an hour of uncontrolled running/playing "is just as bad" as a hour walk with constructive play/retieval practice etc thrown in. if the bad joints etc were true, how do farm dogs always last an age, especially collies who are out all day running mental from a young age. walk your dog for a time which u feel appropriate, 15min walk is probs