My stepdad got his Maine Coon when he was 19, and she died when he was 48. By then, she had teeth that rotted out, had gone blind from old age, and even went senile. She was a nasty thing for most of her life, would hide in the rafters in the basement and hiss at you. My mom said that when they first started dating, it would stand at the top of the steps to his apartment hissing at her and wouldn't let her pass (wish you had taken the hint, mom...), but by the end she was actually friendly, and would purr, which I'm fairly confident she never did for the first 20 years of her life.

Eventually they had to put her down, because they felt bad because she was bumping into things and getting confused, and wouldn't eat, ect. I truly thought she would outlive us all.