Throughout a man's life, his libido reduces gradually, as do all his other vital functions, following the evolution of the energetic metabolism. During the growth period, the anabolism is predominant over catabolism; at the adult phase there is equilibrium and as old age advances, catabolism overtakes anabolism.
Testosterone is the main male hormone, amongst other male hormones, that decisively contributes to the formation of the male body, as a steroid, achieving its highest level in adolescence and beginning of adult life. The hormone levels stay high from 20 to 30 years of age. From 50 years on there is a progressive decline attaining its nadir by 80 years of age. In men that keep a good physical and mental health during their whole life, the decline in testosterone level is the main determinant of the potency loss as age advances. In some men, the loss of the capacity to keep an erection, named erectile dysfunction, starts before losing desire. In most cases though, the opposite occurs.
Unfortunately, most men that get to the age of 80 are not healthy. They are victimized by illnesses like diabetes, hypertension, atherosclerosis and other vascular diseases like varicoceles, which are the main cause of male impotence, including in younger men. Other important causes of male impotence, which are independent from disease and age, are bad habits like smoking, and drinking and eating in excess. Equally damaging to the well functioning of the body, especially of the vases that feed the cavernous bodies, are the drugs used by medicine to treat several illnesses like anti-depressives, anti-hypertensive, tranquilizers, antibiotics, corticosteroids, antifungal, chemotherapy, anti androgenic, diuretics and many others, which can interfere with the erection mechanism or libido.
Obviously, when investigating the cause of impotence the doctor should examine the nature of the partner because it is from her that emanates the stimuli for the libido manifestations and erection. A partner without these emanations, that make her attractive, should not be considered an object of desire.