Complete the expression

[ParanoidUser]

Some day you will be old enough ...

Bonus: Name the author.

[LeleDallas]

To start reading fairy tales again - C.S. Lewis

[peterbaccaro]

The complete expression is, "Someday you will be old enough to start reading fairy tales again.".
This quote is often attributed to C.S. Lewis, and it reflects the idea that no matter how old we get, there's always room for wonder and imagination, including enjoying stories like fairy tales.