teach an old dog new tricks

Change longstanding habits or ways, especially in an old person. For example, His grandmother avoids using the microwave oven-you can't teach an old dog new tricks. This expression, alluding to the difficulty of changing one's ways, was first recorded in 1523 in a book of husbandry, where it was used literally. By 1546 a version of it appeared in John Heywood's proverb collection.