Is it true that Einstein couldn't speak fluently when he was nine and his parents thought he might be retarded?

Yes, it is true that Albert Einstein had delayed speech development and reportedly did not speak fluently until around the age of nine. His parents were concerned about his speech and some even speculated that he might have learning difficulties. However, these early challenges did not reflect his later intellectual capabilities, as he went on to become one of the most renowned physicists in history.