Alys Rivers Is Hundreds of Years Old (Here's How That Makes Sense) HOTD Theory

In House of The Dragon we have gotten to know the witch of Harrenhal Alys Rivers, but certain interview answers given by her actress imply pretty strongly that we have a lot more to learn about her. Gayle Rankin has said more than once Alys Rivers is potentially 400 years old. So let's take a look at some A Song of Ice and Fire magic and lore to see if we can get to the bottom of how this is possible.