There is a lot to be said for your dog having learned behaviors throughout a long lifetime. Over years of behaving in a certain way and being rewarded or punished for it, your dog will develop quite the personality. Some of it is definitely their own “nature,” but a lot of it is also “nurture.” These behaviors are not always easy to change or get rid of, but there is also a big difference between a dog’s personality (learned behaviors) and “new tricks.” Teaching your dog to un-learn behaviors they have been operating with their entire lives can be nearly impossible if the last however-many-years they were rewarded for their actions.
But you can still teach them “new tricks.” Dogs are always able to learn that doing certain actions will give them good treats, or that others may receive a negative stimuli. They can still learn to sit, stay, come, high-five, shake or do whatever else you would like. Dogs are always willing to learn if properly motivated- no matter what their age is. As long as they are physically able to complete the task, and know they will get a nice treat at the end of it, they will happily do it. Dogs just love to please their people- and eat food.
That doesn’t mean, however, that if your dog has learned that scratching at the door means you will let them out, they will stop doing that for a handful of kibble. They have been doing that for years, and for years that has meant their person will stand up and let them out. If their person didn’t want them scratching at the door, that would have been best to establish that when the dog was first learning how to go out. Now, it is unlikely your dog will stop scratching to go out.
You can still try, however! There is never any harm in trying to correct unwanted behaviors. As before, your pup just wants to please you. An older dog is often just stuck a little more in their ways.