Then your conclusion that people over thirty do not change their minds is based on false premis!
There's a difference between "many" and "for all".
Over the decades I've had a number of offline intellectual sparring "partners", where we would argue various issues from different perspectives. In these heated discussions, we mutually agree to not dig in our heels too much. But as we got older, I've found that it was harder to convince the other person of a particular point, regardless of the supporting/dissenting evidence.
Whether consciously or unconsciously, we find ourselves digging in our heels more and more as we got older, than when we were younger. We frequently joke that our minds are "calcifying".
Oh, you misunderstood. I never said your conclusion was wrong. Just that it was based on a false premis.
You just can't make the argument that it is pointless to waste one's time trying to change someone's mind and later claim that you were never trying to change his mind in the first place!
I actually agree...as people get older they can have a tendency to become set in their ways.