In the present work, the concept of exergy is applied in order to propose an index of exergetic age that allows observing changes in life expectancy of a subject based on the exergy destruction throughout the life cycle. To do so, exergy analysis is applied to the human body and smaller internal control volumes for different scenarios where changes in metabolic reactions take place, aiming at determining the destroyed exergy rate as a function of chronological age. From this data, exergetic age index is calculated, enabling to compare the rate of life progression of the subject under different circumstances, based on the idea that there is a maximum value of cumulative destroyed exergy throughout life. The effects of smoking and obesity are evaluated and a reduction of approximately 15 years is observed for smokers, while, for obese people, the index shows an increase. Thus, the identification of obesity as a risk factor is more associated to the development of obesity-related diseases than to the metabolic rate increase and the presence of a thicker layer of subcutaneous fat. Since most of the obesity-related diseases are associated to the cardiovascular system, an exergy model of the human heart is proposed. The model reports an increase of the exergy destruction in case of hypertension that causes a reduction of about four years in life expectancy. Finally, a model of the metabolism of a cancer cell is proposed taking into account the changes in the metabolic paths, from which it is possible to observe a threefold increase of the exergy metabolism of a cancer cell, in comparison to a healthy one. The analysis of tumor progression indicates that, in the absence of treatment, the reduction of life expectancy is about 27 years. Furthermore, in case of treatment, each six months living with the disease causes a reduction of almost four years in life expectancy.