Definition
This idiom suggests that it is exceptionally difficult to teach new skills or change established habits in someone, particularly if they are older.
I tried to teach my grandfather how to use a smartphone, but he just couldn't get the hang of it. You can't teach an old dog new tricks, I guess.
She’s always so set in her ways, I doubt you'll ever get her to change her mind; you know, you can't teach an old dog new tricks.
My dad is not fond of new technology, and I have given up on teaching him how to use the new computer software, you can’t teach an old dog new tricks.