The average human lifespan is a problematic number.

A average human lifespan of 40 doesn't mean that everybody is dead by the time they would hit the 40th year of their life. Let me explain it with an easy example. We have 4 people. 2 of them die as babies and 2 die when they are 80. If we now calculate the average lifespan it's 40 years. As you can see the infant mortality has a huge influence on the average human lifespan. It has the abilitiy to reduce the number to a low appearing number while in reality there are still a lot of people getting old.

This article dives deep into the problems with "average human lifespan" and even talks about the menopause: http://scienceblogs.com/gregladen/2011/05/01/falsehood-if-this-was-the-ston/

What an amazingly reddit thread. Let's talk about the safe, manly statistics of life expectancy while completely ignoring that this question is fundamentally interested in women's experiences in history.

Because of its connection to reproduction and rudimentary birth control, the initiation, cessation, and sometimes resumption of women's menstruation flows through quite the variety of medieval sources. Medical texts, court records, biographies of holy women, modern reconstructions of the gossip on the streets...in the Middle Ages, periods were everyone's business.

With respect to age-induced menopause specifically, medical texts are most concerned with the age at which it typically occurs. There is no universal agreement on a single age--either among different medical authorities, or even in different manuscripts/translations of the same text! Authors do typically note that, as with the age of menarche/onset of menses, the age varies a little ("sometimes more, sometimes less").

Menstruation in medieval medical texts is understood through the theory of the humors: that waste builds up in women's bodies and must be excised through the very natural process of menstruation (the texts stress that this is natural). This apparently explained both onset in adolescence and cessation in middle age: excess waste took time to build up on one hand, but was all excised eventually on the other. An interesting point is that some works distinguish between age at menopause based on the woman's weight. Liber de sinthomatibus mulieum from 12C Salerno (Italy) suggests that menopause occurs around age 50 for most women, 60 or 65 for those who are "excessively moist", but 35 for fat women. This seems curious at first--medieval people were acutely aware that excessive thinness and starvation (whether in times of famine or self-induced through religious asceticism) temporarily stopped menstruation. But here we see the opposite!

Monica Green, probably the leading scholar on medieval gynecology, suggests that fat women were believed to retain excess humors rather than expelling them through menstruation. One interesting note is that the condition known as polycystic ovary syndrome (PCOS) is associated with both weight gain and irregular periods, including complete absence.

Were the numbers connected with reality? That's really hard to tell, since for the Middle Ages our way to attempt reconstruction is to look at the ages when a handful of royal and elite noblewomen stopped having children. Unfortunately, crucial factors are rendered invisible here: did women have more say in 'birth control' as they got older and more confident, as heirs survived to reasonable assurance of adulthood? Christine Klapisch-Zuber for Italy and Anneke Mulder-Bakker for northern Europe have both suggested this pattern of increasing voice and agency with age. Did men turn to younger, prettier women as their wives aged? De ornatu mulierum provides a recipe for an herbal mixture that wives should give to their husbands who no longer desire them. Chaucer's "Merchant's Tale" has a character sling insults at a thirtysomething woman as washed up, dried up, and infertile.

It's likewise hard to reconstruct how women themselves perceived menopause. Every now and then, someone (usually a woman) is noted in court records as selling or providing herbs to "restart" menstruation when it has stopped. (This would be provided by way of establishing who the witness is, not the crime except in cases of fraud). The typical interpretation here, however, is attempts at abortion or a cure for infertility, not undoing menopause. On the other hand, practices like long periods of breastfeeding are linked with primitive attempts at birth control (in medical texts, at least), and as noted above, women did seem to taper off having children as they got older. Was menopause greeted with relief at being able to have sex without risk of pregnancy? Was it a curse marking the end of fertility? How did women understand hot flashes? (An interesting note on this point is that the male parallel to menstruation as far as expelling waste was said to be sweating.)

Unfortunately, most of the more "experiential" sources on cessation of menstruation relate to accusations of infanticide (fama of amenorrhea beforehand offering proof of pregnancy) or holiness (amenorrhea proving actual paucity of food consumption), not age. Our few women writers don't discuss their own bodies. In the Latin Middle Ages, your neighbor's last period was everyone's business. Your own? Secretum meum mihi, secretum meum mihi.

In addition /u/OpenOb's comment, this comment from /u/roxinos on ancient lifespans would be relevant as well: https://www.reddit.com/r/AskHistorians/comments/4bxwup/ancient_life_expectancy/d1dg2so

Once you consider average life expectancy at some period after infancy and early childhood, say, life expectancy at 15, then the length of time someone could reasonably expect to live is not dramatically different than modern lifespans.