Old dog new trick
Saying you can or can't teach something to someone once they've gotten past the time when they learned their ideals/ways. Saying you can or can't change someones mind about their long term opinions or beliefs. can be referring to a human as well.
Example:
A: my dog won't listen when I tell him to sit!
B: yeah, you can't teach an old dog new tricks.
A: but can't you just hear me out on this, B?
B: no! I made up my mind a long time ago.
A: *sigh* you can't teach an old dog new tricks.
A: I'm 70 years old but I just learned rock climbing!
B: you can teach an old dog new tricks!
A: my dog won't listen when I tell him to sit!
B: yeah, you can't teach an old dog new tricks.
A: but can't you just hear me out on this, B?
B: no! I made up my mind a long time ago.
A: *sigh* you can't teach an old dog new tricks.
A: I'm 70 years old but I just learned rock climbing!
B: you can teach an old dog new tricks!