I don't know if this a suitable question. However lately I have been looking into family life of the 19th century a bit and noticed that once women were married, they were very quickly having children. Sometimes children would follow 1-2 years after the last child.
However I noticed that at around 35 they all of a sudden stopped having children. For example tsaritsa Alexandra was around 32 when she had her last child Alexei. In peasant families this was also the case that women stopped having children around 35.
Today women can have children when they are older, and hit menopause around 47, so I wonder that back then, when there was no birth controll they would stop having children at a certain age. How?
It's a perfectly suitable question here: I consider childbearing age one of the most important factors in history, so I'd welcome more like it!
But I'd say the long-run change has actually been in the other direction: the data available suggest that until the late 20th century the tendency was toward less childbearing in later reproductive years: while there's been a reversal in recent decades, the current upturn remains modest and will itself level off.
This makes sense when you think of fertility control (natural or artificial) being used after (say) the second or third child: the averted higher-order births (the fourth, fifth etc, and increasingly the third) were more likely to have occurred in the 30s or 40s than in the 20s. It's only recently that we're again seeing a significant impact from lower-order births instead being deferred from the 20s to the 30s.
For England Wrigley et al (English population history through family reconstitution 1580-1837, CUP 1997) find a mean age at maternity of 33 years in 1600-1725 and 31.3 in 1775-1837. The latter is close to the western European average today, but this figure has itself risen by nearly four years since the late 1970s, so until then the trend again appears to be downward.
And while a pronounced falling-off of natural fertility in the late 30s seems to be something of a universal a human constant, an average childbearing age of 33 or even 31 (the latter probably nearer to the pre-industrial western European average) alone suggests that a considerable number of births must have come after age 35, birth intervals at this stage averaging just over 2½ years.
As well as a lowering of the overall average age and a fall in overall fertility, there's been a compression in age-specific rates, with a greater proportion of childbearing tending in the 20th century to cluster at ages 20-34. Among women completing their 50th year, a fifth or more of births occurred at ages 35-49 at fertility rates characteristic of the pre-industrial period, but only a tenth when Europe hit replacement fertility in the 1970s.
So your finding seems rather surprising, and I'd be interested to know more. I'd welcome further information about your peasant sample, notably the area and period: conditions of course varied widely, and local anomalies can't be ruled out, but it seems to differ markedly from the long-run general pattern, which doesn't mean it's wrong.