First you need to research the relative proportions of male and female births, and then, just to complicate matters, I have a vague memory that, for some reason, one sex was slighly more likely than the other to succumb to death in infancy and childhood.
The result of that little exercise, and I'm near certain that Google will assist

, will provide info on any imbalance in the sexes, i.e. available partners for marriage.
Secondly, for most folk in the 18th and 19th centuries, and some decades into the 20th C, the man didn't consider marriage until he could support the resultant family; meaning that the most frequent age at marriage for a man was late 20s, early 30s ......
If he couldn't find a partner, and remember that most folk married partners of like age, then it wouldn't take that long before the man was into his mid/late 30s and on the way to becoming a confirmed bachelor, and perhaps no longer that interested in going out and locating a wife who was much younger than him.....
Remember as well that there could be "competition" in the "market place", so to speak, with widowers with young weans competing for the affections of available young ladies. From a security point of view, many such young ladies might prefer, - I'd suspect, but can't prove it, - to "give their affections" to an older man who had already demonstrated that he could "hack it" in terms of earning a good living! Very much a generalisation
In addition, it was probably quite often the case that the unmarried son or daughter in a family eventually took on the responsibilities of looking after the parents to the exclusion of marriage.
David