20 years, reckoned from conception. However, boys under that age are allowed to ordain as novices (sāmaṇera), performing a ceremony such as shinbyu in Myanmar. Novices shave their heads, wear the yellow robes, and observe the Ten Precepts. Although no specific minimum age for novices is mentioned in the scriptures, traditionally boys as young as seven are accepted. This tradition follows the story of the Buddha's son, Rahula, who was allowed to become a novice at the age of seven. Monks follow 227 rules of discipline, while nuns follow 311 rules. In most Theravāda countries, it is a common practice for young men to ordain as monks for a fixed period of time. In Thailand and Myanmar, young men typically ordain for the retreat during Vassa, the three-month monsoon season, though shorter or longer periods of ordination are not rare. Traditionally, temporary ordination was even more flexible among Laotians. Once they had undergone their initial ordination as young men, Laotian men were permitted to temporarily ordain again at any time, though married men were expected to seek their wife's permission. Throughout Southeast Asia, there is little stigma attached to leaving the monastic life. Monks regularly leave the robes after acquiring an education, or when compelled by family obligations or ill health. Ordaining as a monk, even for a short period, is seen as having many virtues. In many Southeast Asian cultures, it is seen as a means for a young man to "repay his gratitude" to his parents for their work and effort in raising him, because the merit from his ordination is dedicated for their well-being. Thai men who have ordained as a monk may be seen as more mature and suitable husbands by Thai women, who refer to men who have served as monks with a colloquial term meaning "ripe" to indicate that they are more mature and ready for marriage. Particularly in rural areas, temporary ordination of boys and young men traditionally offered peasant boys an opportunity to receive free education in temple schools with sponsorship and accommodation. In Sri Lanka, temporary ordination is not practised, and a monk leaving the order is frowned upon but not condemned. The continuing influence of the caste system in Sri Lanka plays a role in the taboo against temporary or permanent ordination as a bhikkhu in some orders. Though Sri Lankan orders are often organized along caste lines, men who