The "average age of brides in Russian history" is quite the timespan to observe. For that it might be said it varied, a lot, but a lot around basically the same age window: very young. Although contemporaries often noted that an age below sixteen was not that good for a variety of reasons. Peasant women giving birth below that age rarely had surviving off-spring, marriages according to custom were often quite unhappy, etc.
From the earliest times in Russia, marriage represented the most important point of transition for women, from a position of dependence and inequality to emancipation. In the eighth to the tenth centuries, a ritual of abduction was the usual means of concluding a marriage. The oldest chronicles report that young men would "carry off" their brides during "games." The Russian pagan god of marriage, Lado, sanctified these "games," which were organized near springs or rivers in late spring or summer. According to the chronicles, the "abduction" took place with the mutual consent of the bride and groom: "each man carried off a wife for himself, the one with whom he had come to an agreement." The common people retained this form of marriage in the countryside for centuries after the adoption of Christianity. Traces of marriage by "abduction" can still be found in folklore and in rituals that survive to the present day for example, the custom of carrying the bride over the threshold.
More formal wedding ceremonies arose later. In the tenth century, with the development of more complex social structures, a new contractual form of marriage appeared. The parents and relatives of the bride would bring her to the groom's house, and on the next day they would bring her dowry. This form of marriage gave greater weight to the family's choice of spouse than to the bride's, and it also emphasized the financial arrangements surrounding the marriage.
From about the thirteenth century on, it became customary for the marital contract to be signed not only by the adult members of the clan but also by the bride and groom. Sometimes the bridal couple made all the arrangements themselves. Private correspondence, written on birchbark (which archeologists have uncovered in Novgorod and other Russian cities), testifies to this. One such letter, from a man to a woman and dating from the twelfth century, reads, "From Mikita to Ulianitsa. Marry me! I want you, and you want me. Ignat will be the witness. … "But it was more customary for the parents to make the arrangements for the wedding. The Russian tradition forbidding the groom to see the bride between the betrothal and the wedding day represents a survival of this custom. The etymology of the Russian word for "bride," nevesta, also reflects this tradition; it means, literally, "unknown woman."
Orthodox Christian canons set a number of conditions for the establishment of a valid marriage. The first of these concerned age; ecclesiastical law prohibited the marriage of girls under the age of twelve and boys under the age of fifteen. On average, girls married at the age of thirteen or fourteen, but chronicles report cases when parents arranged marriages for children eight or even five years of age. But such marriages took place only among the aristocracy and were concluded for political gain.
Young marriages offered several advantages. First, because of the short life expectancy (less than 50 years), early marriage maximized the reproductive period of the couple's life. In addition, a girl who was not yet grown up could be expected to be more tractable, more willing to obey her parents and her husband.
Early in the eighteenth century, the age of marriage for girls remained low, about twelve years, when they were still dependent upon their parents not only for their consent but also for their knowledge of adult responsibilities. The requirement in the Law Code of 1649 that girls not marry before the age of fifteen was rarely observed.
Judging from memoirs, most gentry men chose wives who were twelve or thirteen years old; Peter the Great himself announced that his daughter Elizabeth (the future empress) had attained her majority when she reached the age of twelve. However, the custom of early marriage changed in the course of the eighteenth century; the age of marriage increased, especially in the cities among the well-to-do strata of society. By the end of the eighteenth century, brides in cities were usually fifteen to eighteen years old, and even in villages young marriages were becoming more and more rare. The impetus for the rising age of marriage for peasant women is found more in practicality than in concern for their emotional well-being: only full-grown women had the physical strength to undertake the heavy field work, livestock herding, and household crafts expected of peasant wives. Thus in the countryside in the eighteenth century, the age of marriage for girls became fourteen years and for boys, sixteen years.
Natalia Pushkareva: "Women in Russian History: From the Tenth to the Twentieth Century", Sharpe : Armonk, London, 1997.
N.L. Pushkareva & Eve Levin: "Women in Medieval Novgorod from the Eleventh to the Fifteenth Century." Soviet Studies in History, vol. 23, no. 4 (1985), pp. 71-90.
Engel, Barbara Alpern. "Peasant Morality and Pre-Marital Relations in Late Nineteenth Century Russia." Journal of Social History, vol. 23, no. 4 (1990), pp. 695-714.
Claus, C. Die Stellung der russischen Frau von der Einführung des Christentums bei den Russen bis zu den Reformen Peters der Grossen. Munich, 1959.
Clements, Barbara Evans, Barbara Alpern Engel, and Christine Worobec, eds. Russia's Women: Accommodation, Resistance, Transformation. Berkeley, 1991.
Confino, Michael. "Russian Customary Law and the Study of Peasant Mentalités." Russian Review, vol. 44, no. 1 (1985), pp. 35-43.
Costlow, Jane T., Stephanie Sandler, and Judith Vowles, eds. Sexuality and the Body in Russian Culture. Stanford, 1993.
Frey, Linda, Marsha Frey, and Joanne Schneider, eds. Women in Western European History: A Select Geographical and Topical Bibliography. London, 1982.
Goscilo, Helena, and Beth Holmgren, eds. Russia, Women, Culture. Bloomington, 1996.
Kon, Igor, and James Riordan. Sex and Russian Society. Bloomington, 1993.
Lewitter, L.R. "Women, Sainthood, and Marriage in Muscovy." Journal of Russian Studies. vol. 37 (1979), pp. 3-11.
Approaching modernity these average ages grew somewhat larger:
Alexandre Avdeev & Alain Blum & Irina Troitskaia: "Peasant Marriage in Nineteenth-Century Russia", Population, 2004/6 (Vol. 59)
Table 6 - Mean age at marriage according to various sources, Vykhino estate (1815-1861)
And from there, the average age for first marriages fluctuated significantly, influenced by war and communism, with communism favouring again a quite young age for a while
Alexandre Avdeev & Alain Monnier: "Marriage in Russia: A Complex Phenomenon Poorly Understood", Population: An English Selection, Vol. 12 (2000), pp. 7-49
One often observes increasingly late first marriage, a rise in celibacy, a strong increase in the frequency of divorce (when permitted by law), the development of cohabitation outside marriage and an increase in births outside marriage. In Russia, the age on first marriage fell continuously from 1960 to 1990; only over the last few years has the trend reversed and most of the changes just mentioned are now present, with the exception of just one: cohabitation outside marriage, which housing problems prevent from developing as a substitute for marriage.