When it comes to having children, there is a key factor that differentiates women from men: the biological clock. Postponing having a family certainly has psychological implications and consequences for men, but it has none - or at least infinitely fewer - from a physiological point of view. The man’s capacity to procreate, technically understood as the ability to produce enough sperm of sufficient quality and in sufficient number to make not only possible but probable the fertilisation of an ovum in the event of unprotected sexual intercourse, is certainly more prominent at a young age. But it remains basically stable even during middle age (between the ages of 40 and 65), and does not decline much later, in the third age (commonly understood as the decade between 65 and 75). Apart from possible erectile problems, or other common ailments such as prostate cancer, men stay fertile for their entire lives.
This is not the case for women.
In the document Age and Fertility - A Guide for Patients Published in 2012 by the American Society for Reproductive Medicine, there is data on the decline in fertility that is inextricably linked to age. A woman's best years from a reproductive point of view are between 20 and 30, the document states. Fertility gradually declines in the 30s, specifically after age 35. In particular, “each month that she tries, a healthy, fertile 30-year-old woman has a 20% chance of getting pregnant. That means that for every 100 fertile 30-year-old women trying to get pregnant in 1 cycle, 20 will be successful and the other 80 will have to try again. By age 40, a woman’s chance is less than 5% per cycle, so fewer than 5 out of every 100 women are expected to be successful each month” on the first attempt at pregnancy.
This is the main reason why, should someone wish to have children, the age at which they choose to start trying to have them is significant, especially for women; and why the rise in the average age at first child recorded worldwide, especially in advanced countries, is significant and does not favour women wishing to become mothers.