set in (one's) ways
Inflexible; unwilling to change. Grandma will never retire—she's been a teacher for 50 years and is totally set in her ways. You'll never convince him to change, he's too set in his ways now.
set in your ways
If someone is set in their ways, they have very fixed habits and ideas which they are unwilling to change. At 76, he was too set in his ways to change. His brother's wife made no secret of the fact that she thought him boring and too set in his ways. Note: This expression is usually used to show disapproval.