tatah parinate kale
gam putraya gato vanam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thereafter, when the time was ripe, when Sudyumna, the king of the world, was sufficiently old, he delivered the entire kingdom to his son Pururava and entered the forest.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
According to the Vedic system, one within the institution of varna and asrama must leave his family life after he reaches fifty years of age (pañcasordhvam vanam vrajet). Thus Sudyumna followed the prescribed regulations of varnasrama by leaving the kingdom and going to the forest to complete his spiritual life.
Thus end the Bhaktivedanta purports of the Ninth Canto, First Chapter, of the Srimad-Bhagavatam, entitled “King Sudyumna Becomes a Woman.”