The moment when old age actually begins is not represented by any fixed threshold and varies very much in keeping with the particular era or place in question and is often defined by the rules of each society, establishing a sort of 'rite of passage' with the creation of a new living status. In industrial and postindustrial societies this passage depends less and less on the onset of old age and all that this entails--less physically able, a reduced intellectual capacity, and is increasingly linked to an economic and social value attributed to the individual on the basis of a change in occupational status following retirement. This change is usually classified according to outdated rules, which are no longer acceptable, so that the age at which one's working life ends can often coincide with a stage when the individual concerned is by no means old ( Livi Bacci , 1987; Egidi, 1990).
Fixing a particular age to mark the onset of physical decline is by no means easy. This decline is the cumulation of individual experiences which, either earlier or later, affect health and physical capacity. It is, for example, closely linked to one's social origins, which negatively or positively affect the life of the individual: a miner, in all likelihood, may already be in a fairly precarious physical condition by the time he is 50, while an individual from a higher social class may not feel his seventy or eighty years at all ( de Beauvoir, 1970).
It is obvious that the age threshold for the onset of old age for a given generation depends on the average social, economic, and cultural conditions of those who make up the cohort, the adopted life-styles and awareness of aspects related to their health, i.e. all factors which help modify the rhythms of the individual ageing process. All improvements made in recent years in economic, social, and cultural status have consequently raised the age threshold even higher.
It is equally evident that yesterday's old people do not represent those of today, nor will either of them be representative of those of the future, who belong to cohorts whose working, social, and cultural life histories could favourably affect their physical and mental health status. This conviction is given further backing by analyses made of the recent health transition in Europe, marked by a major decline in mortality among the elderly: a decline mainly due to favourable trends in diseases of the circulatory system and