Can gynecomastia become less noticeable with exercise?

Thanks for your inquiry.  Exercise may decrease the amount of fatty tissue on the chest (and elsewhere on the body), but if there is glandular tissue it will not decrease with exercise.

At 14 it is possible that the problem will resolve.  Exercise will help define the structures of the chest and upper body in a way which will improve your appearance.  It is possible that exercise alone will not resolve the gynecomastia.