Carbonylation due to oxidation and glycation is an important biochemical cause of degenerative diseases and aging. While the enigma of aging is understood as a result of molecular dysfunction due to the failure of maintenance systems, a brief history of the interpretation of aging mechanisms and the exact biochemistry connecting entropy and biological aging is addressed. Lipofuscin formation mechanisms resulting in irreparable accumulative changes represent the most important aging- related alterations of entropy increase in biological kingdom, which is very different from the damage-based “aging” process of inorganic materials. A fifth level of aging mechanism investigations that highlights the importance of functional groups of biochemistry, the “missing codes” of life science, is put forward in this review. Significance and validities of such ‘life codes’ in biology beyond genomic and proteomic concepts has also been clarified. An open-minded consideration of functional groups of biomolecules, such as carbonyl groups, may help to explain the mechanisms of fatigue and sleep in terms of neurobiochemistry and biological pharmaco-medicine.