I think Persian and a handful of other languages are the outliers. The main difference between old, middle, and modern Persian is the writing system.
Old Persian is quite hard to read and understand for a modern Persian speaker, but if one spends a few weeks learning the writing system of middle Persian (called Pahlavi), they will be able to understand a lot of texts written before 500 AD.
Old Persian is quite hard to read and understand for a modern Persian speaker, but if one spends a few weeks learning the writing system of middle Persian (called Pahlavi), they will be able to understand a lot of texts written before 500 AD.
https://en.wikipedia.org/wiki/Pahlavi_scripts