This is what I the book says; do what you will. Younger age could alleviate some of the dangers I guess, as was stated:
Pullovers are supposed to "expand the rib cage." This assumes that ribs will somehow lengthen, or that cartilage will change to allow expansion to take place. Bone just doesn't work that way. Training of various types can change the vital capacity of the lungs- the quantity of air that can be exhaled by the fullest
expiration after making the deepest inspiration. However, much of this change results from the learned ability to use available lung space and from improved control of the diaphragm. Neither change translates into a larger rib cage. Think about it-Despite the trememdous vital capacities of opera singers and trumpet players, few (if any!) could win a bodybuilding contest.
Pullovers won't expand your rib cage; but there's a good chance that, in time, doing them will cause shoulder or other injuries. One example: The exercise can stretch the connective tissue that forms the vertical "line" between the abs. If that tissue tears, you have a hernia of the median rectus, which produces a slight bulge in the center of your abs that increases in size when you strain. A hernia of the median rectus is of little clinical significance, but it's certainly not what you were trying to develop! Pullovers also put tremendous stress on the posterior aspect of the shoulder; even before you sustain a clinical injury, they can cause a great deal of pain.
The bottom line: Pullovers won't enlarge your ribcage, and their high potential to injure the rotator cuff and other structures far outweighs whatever minimal muscular gains they may promote.
