This is not am impossible task but you can't train an older dog like you would train a puppy. You have to be a little bit stricter on an older dog, this is because they have a lot more intelligence than a puppy and know how to manipulate you. An older dog is more likely to do something if he thinks its his idea rather than yours, for example if he goes to sit, say sit and then praise him, he will soon think it was his idea and if you keep on repeating this process sooner or later you will have him sitting on command. This process will work for many commands, like fetch, come, stay and heel.
You may find that your older dog is particularly easy to train, some dogs have a streak of stubbornness which means they will not train as easily as others but some are more susceptible to training methods. Training an older dog will of course be more difficult but bad habits need to be broken. Your dog will thank you for it, the end result and the relationship built will be well worth the trouble.
Training an older dog can often be a grueling task but try making it enjoyable by joining a local class (they are not just for people with new puppies) you may even try to get some support from family or friends, invest in some training products such as toys and treats, you may even want to consider a training school, but one thing is for sure once you've taught your dog what he needs to know the bond between you will grow and you will soon become inseparable.
