On the flip side, have you ever considered the problem may not be with them, but with your approach? People don't like being wrong, even when they are wrong, and they don't generally like confrontation, especially when what you're asking them to confront is reality. It's a quirk of psychology that attacking someone's firmly held beliefs or ideas, even with a solid argument, good evidence, and the absolute truth on your side, will only serve to reinforce their wrong beliefs. If you want to convince someone, you need to feed the evidence and the arguments to them subtly. You need to get them curious, and get them thinking, and allow them to come to the conclusion themselves so they won't have to suffer defeat. It's hard, but I managed it once! And she was over thirty.
When I was younger, my intentions were rarely to ever change people's minds. My underlying intention was to get under the person's skin.
Then your conclusion that people over thirty do not change their minds is based on false premis!
I'm happy people are finding the thread valuable, I know I'm learning a lot by reading it.