I recently moved in with my girlfriend and she has a 6 year old border collie. The dog has never really been trained before. "Sit" and "Lay Down" are the only 2 commands he knows. I'd like to teach him a few more tricks but I'm not sure if I should even waste any time on that because I've heard that it is much harder to teach an older dog. I'd like to know if it's possible because I'm willing to devote as much time on that as needed.