Final answer:
The information provided does not contain enough context to accurately determine what Irving did before turning 28; the references mention other aviators, but not Irving's specific activities.
Step-by-step explanation:
The question likely refers to a historical figure, but without a specific name, it's challenging to determine exactly what Irving did before turning 28. However, based on the provided reference, we can rule out options (a) and (b) because there is no mention of Irving serving in the U.S. Air Force nor working as a commercial pilot before this age. The reference does touch upon the subject of aviators and their activities related to flying, such as Charles Lindbergh and Bessie Coleman, but it does not provide clear information about Irving's activities before he turned 28. Therefore, without additional context or a specific reference to Irving's actions before the age of 28, providing an accurate answer is not possible.