You can't teach an old dog new tricks

something that you say which means it is difficult to make someone change the way they do something when they have been doing it the same way for a long time You're never going to teach your father at the age of 79 to use a computer. You can't teach an old dog new tricks, you know.

Getting people to change their habits or acquire new skills is impossible. Puppies are teachable, but older dogs are less apt to be able to be trained, or so popular wisdom had it. By the same token, an octogenarian who has read the morning newspaper for decades is unlikely to be willing, much less eager, to switch to the online edition.