Which sentence is most clearly written?

The most clearly written sentence provides a straightforward construction that eliminates any ambiguity. It begins with a time marker, "When Dave was seventeen," which places the reader in the context of the event right away. This phrasing emphasizes the chronological order of events before introducing who is involved and what was said, making it easier for the reader to follow the narrative.

Additionally, the second sentence utilizes simple and direct language, which enhances readability. This clarity is particularly important for conveying information effectively. By positioning the age information right at the beginning, the reader can quickly grasp the key details without wading through additional phrases, as found in the first option, which starts with "At the age of seventeen." This formulation can feel slightly more cumbersome and less direct compared to the alternative.

Overall, the clear construction and concise wording of the second sentence make it the better choice for effective communication.