You can't teach an old dog new tricks
ɔ̃ nə ʃɑ̃ʒ paz œ̃ vjø ʃjɛ̃
In French On ne change pas un vieux chien.
This idiom is a common expression in French, conveying the idea that it's difficult to change someone's ingrained habits.
Example
"Il est trop tard pour lui apprendre à faire du sport, on ne change pas un vieux chien."
