hi how can v tell the age of dog,e.g bullmastiff,i asked this question before i had no response.pls advice.his got no papers,person who had him said his 2 years,but i am not sure,only reason i rehomed him is he did not look happy there.
                          thank you

The usual way of telling is by the condition of his teeth. You'll still only be able to get a 'guesstimate' - if he's got all his adult teeth he's more than 6 months, if all his teeth are still quite white (though they may be dirty) he's probably under 5, if the teeth are quite yellowy (even though they may be clean) then he's probably older than that. What does the vet reckon?

There is no way you can tell by just looking at a dog.  X-rays would reveal whether the growth plates are closed, the level of wear on the joints etc for a guestimate to be made.  Looking at the teeth can also show you if the dog is a pup or adult, but as dogs wear their teeth differently and a lot will depend on diet, this si not very reliable either.

At the very best you can only ever guess.  Not only looking at the color of the teeth but at the wear.

http://www.geocities.com/Petsburgh/Zoo/1224/canineteeth.html