Here's the proximate physical implication of the ratio (from the Wikipedia article on NADH).
The balance between the oxidized and reduced forms of nicotinamide adenine dinucleotide is called the NAD+/NADH ratio. This ratio is an important component of what is called the redox state of a cell, a measurement that reflects both the metabolic activities and the health of cells. The effects of the NAD+/NADH ratio are complex, controlling the activity of several key enzymes, including glyceraldehyde 3-phosphate dehydrogenase and pyruvate dehydrogenase. In healthy mammalian tissues, estimates of the ratio between free NAD+ and NADH in the cytoplasm typically lie around 700; the ratio is thus favourable for oxidative reactions. The ratio of total NAD+/NADH is much lower, with estimates ranging from 0.05 to 4. In contrast, the NADP+/NADPH ratio is normally about 0.005, so NADPH is the dominant form of this coenzyme. These different ratios are key to the different metabolic roles of NADH and NADPH.
So here's my question: how does this manifest in vertebrate aging? Is it something that's simply the resultant of other aging processes, or can the ratio also contribute to aging in a certain way?