For their study to be valid in proving that exercise prolongs 'youthfulness' it requires that they be meeting the species normal exercise limits before expanding on them, otherwise they're actually performing a study on how sedentary lifestyles reduce youthfulness.

This is a scientific study that isn't being accurate about what it's even studying, which makes me instantly dubious of any of its results.

That is assuming the definition for exercise is any level of activity above the standard and expected activity level of a species.

Put into context, your reasoning implies that a rat running around all day looking for food is not exercise.