Sometimes the opportunities miss you and you do not even realize it. Many young people do not know how drastically the possibility of pregnancy goes down for a woman over time.
The same goes for men. It is not as drastic, but the issues accumulate. You cannot even be a sperm donor after year 32-36 (depending on the clinic).
There are many opportunities that are not equal thought the life. You will not be the best athlete after 40. You will not be the best thinker after 60. And many more.
The sooner you realize the milestone, the more good pressure you put on yourself to not miss the opportunities.
Find a wife, exercise, join clubs, study, have kids, do well at work. The clock is ticking.