Ordination In South East Asia
Throughout South East Asia, it is very common for young men to become bhikkhus (or novices) for a short period of their life. Traditionally this occurs during the three months of the Rains Retreat, after which they disrobe and return to lay life, hopefully knowing and appreciating much more about the bhikkhu life — and probably having friends still in the monastery whom they can visit for advice. In Thailand this means that while a small proportion of bhikkhus will spend all their life in the robe, many more Thai men will have tasted the life.
Such an ordination is also a rite of passage, for it is a family, even a village event with many people joining in to see the young man off into this new stage of his life.1 The new monk will frequently visit his former home on his daily alms round so his ordination has a wider influence, showing the continuing possibility of living the Holy Life started by the Lord Buddha so long ago.
It may also be considered a way for the young man to show his gratitude to his parents and grandparents, for they are thought to participate and share in the merit he makes through his ordination. Also, some men might ordain for a time before marriage — one way for the young man to prove his maturity to his fiancee — and then again later in life after retirement.
For an interesting description of this aspect see Burmese Buddhist Culture.