In Thailand, all young males (including members of the royal family) were required to become Buddhist monks, even if only for a short time, before they turned 20. This technique is no longer as popular as it once was, though.
Being ordained in Thai Buddhism is a temporary commitment that lasts for one week to a few months, unlike being ordained as a Christian monk or priest, which is considered to become your new way of life.
This can be done at any stage of life, such as when you reach 18, just before getting married, or following a period of adversity or criminal activity in which the person seeks some sort of redemption by joining the monastery.
There are some roles, like being the head of a rural village, which you cannot do without having spent time in a monastery. Being ordained into a Buddhist monastery enables the man to acquire greater respect from family, friends, and society at large.
All Thai males who practice Buddhism are expected to join a monastery at some point in their lives in order to learn the Dharma and gain a better understanding of their faith. This is frequently done prior to marriage as a means to benefit the man's parents and his future spouse.
Entering the monastery also demonstrates to your prospective wife's family that you are a respectable man who will be devoted, considerate, and caring. Spending time in a monastery is also meant to demonstrate your ability to guide your prospective wife and family during your lifetimes together.
A very old-fashioned rite of passage, entering the monastery is becoming less and less common as time passes. However, it's possible that wives are more concerned with the man's work and the money in his pocket than his duty to his or her parents, as most young men still choose to become ordained as monks in order to please their parents or the parents of their future spouse.
It will be fascinating to see if this custom lasts for another 10, 20, or more years.
Why not inquire if he has received ordination into a Buddhist monastery from a local man you encounter while traveling in Thailand and learn about his experience? Getting a first-hand account of someone's thoughts and beliefs is always fascinating; just remember to treat them with respect as you do so.