This increase in premature marriages is, speaking generally, a symptom indicative of the premature awakening of sexuality in our own time, a phenomenon which we shall discuss more fully later. Such an occurrence as the elopement of a girl aged fourteen with a boy aged fifteen, the pair having already for some time been engaged in an intimate love-relationship, and having finally come to the conclusion that they could no longer live apart, is by no means a great rarity.[176] No detailed argument is needed to show that persons completely wanting mental and moral maturity are not suited for marriage, which can only be regarded as offering some security for endurance and life happiness, when it is the union of two fully-developed personalities. In this respect it seems to me that the regulations of the Civil Code are not at present sufficiently strict. A second notable factor in the causation of unhappy marriages is an excessive =difference between the ages= of husband and wife, and in this respect it is quite an old experience, that a marked excess of age on the part of the husband has a less unfavourable influence than a similar excess on the part of the wife. This observation harmonizes with the fact that men can preserve sexual potency up to the most advanced age--even in a centenarian active spermatozoa have been found[177]--that such old men can have complete sexual intercourse, and can procreate children; whereas in women, at the age of forty-five to fifty years, with the cessation of menstruation the procreative capacity is extinguished, though not, indeed, the capacity for sexual intercourse and for voluptuous sensation. Naturally, in this connexion we are not alluding to quite abnormal cases, such as a premature impotence in the husband, or other morbid conditions in either husband or wife. We are considering merely the normal physical difference in age. Metchnikoff lays great stress upon this physical disharmony between husband and wife. He insists upon the fact that in the man sexual excitability generally begins much earlier than in woman, and that at a time when the woman stands at the acme of her needs the sexual activity in the man has already begun to decline; but this is only the case when the husband was notably older than the wife when the marriage was contracted. A difference of five or ten years in this respect is a small matter; but a difference of ten or twenty years may be of serious significance. Generally speaking, in the case of marriages which are intended to be of lifelong duration, the difference of age should never exceed ten years.