odds of it happening eventually, go up the longer you live.
Despite this DNA replication being highly controlled and very accurate, the sheer number of times it is performed in the lifespan of a person (estimated to be 10,000 trillion times!) means the introduction of a significant number of errors into the DNA of some of our cells from this fundamental process is inevitable. source
Supernatural had a guy who was immortal but kept aging/developing disease. He tried to take Sam’s eyes to replace his own