Dogs of any age can be taught to sit. It just takes a little patience and a few clever techniques. Begin with a handful of treats that your dog likes. Put a leash on your dog so that you have him in front of you.
Holding a treat in one hand, place it close to your dog’s nose, but out of reach of him jumping up and grabbing it. Move the treat slowly up over his head. The plan is to lure him into the sitting position and use a hand signal to do it, as you say, “sit.” As soon as he sits, say “yes!” Give them the treat and praise them gently so that they will not get too excited and jump up. Release them by saying “okay.” Do not give out a treat at this time or you will be rewarding the action of getting up. Repeat this process a few times for a few days and your dog will begin to understand your command.
Another way to teach your dog to sit is to have the treat in your hand and push his bottom to the floor while you say “sit.” You need to immediately give him a treat to reward his behavior. When he sees he is rewarded, he will respond as you continue to practice this teaching method. When he responds consistently to your command to sit, he will expect a treat each time. This will be the time to back off on rewards and praise. Only praise and reward him every third time. As you praise him less and less for sitting on command, he will begin to obey without being rewarded and you will have accomplished your goal.