Women's fertile lives are very much defined by their reproductive cycles. This is from their first menstruation (menarche) to the time of menopause.
Unlike women, men do not see their fertility reduced so dramatically when they reach a certain age. Their biological clock does not stop so abruptly, but rather slowly, allowing them to continue having children well into old age.
However, this does not mean that they keep their fertility intact, as it decreases and so does their seminal quality. It has been seen that men in their 50s have reduced sperm quality compared to men in their 30s. This is due to the fact that the concentration of testosterone is decreasing, and therefore the effectiveness of spermatogenesis (the creation of spermatozoa) is decreasing.