Kṛṣṇa's age, His transcendental bodily features, His beauty, and His mildness are qualities pertaining to His body. There is no difference between Kṛṣṇa and His body, and therefore the transcendental features pertaining to His body are the same as Kṛṣṇa Himself. But because these qualities stimulate the devotee's ecstatic love, they have been analyzed as separate causes of that love. To be attracted by the qualities of Kṛṣṇa means to be attracted by Kṛṣṇa Himself, because there is no real distinction between Kṛṣṇa and His qualities. Kṛṣṇa's name is also Kṛṣṇa. Kṛṣṇa's fame is also Kṛṣṇa. Kṛṣṇa's entourage is also Kṛṣṇa. Kṛṣṇa and everything related with Kṛṣṇa which gives stimulation to love of Kṛṣṇa are all Kṛṣṇa, but for our understanding these items can be considered separately.
Kṛṣṇa is the reservoir of all transcendental pleasure. Therefore, the impetuses to love of Kṛṣṇa, although seemingly different, are not actually distinct from Kṛṣṇa Himself. In the technical Sanskrit terms, such qualities as Kṛṣṇa's name, fame, etc., are accepted both as reservoirs of and stimulation for love of Kṛṣṇa.
Kṛṣṇa's age is considered in three periods: from His appearance day to the end of His sixth year is called kaumāra; from the beginning of the sixth year up to the tenth year is called paugaṇḍa; and from the tenth to the sixteenth year is called kaiśora; after the beginning of the sixteenth year, Kṛṣṇa is called a yauvana or a youth, and this continues with no change.
As far as Kṛṣṇa's transcendental pastimes are concerned, they are mostly executed during the kaumāra, paugaṇḍa and kaiśora periods. His affectionate pastimes with His parents are executed during His kaumāra age. His friendship with the cowherd boys is exhibited during the paugaṇḍa period. And His friendship with the gopīs is exhibited during the age of kaiśora. Kṛṣṇa's pastimes at Vṛndāvana are finished by the end of His fifteenth year, and then He is transferred to Mathurā and Dvārakā, where all other pastimes are performed.
Śrīla Rūpa Gosvāmī gives us a vivid description of Kṛṣṇa as the reservoir of all pleasures in his Bhakti-rasāmṛta-sindhu. Here are some parts of that description.
Kṛṣṇa's kaiśora age can be divided into three parts. In the beginning of His kaiśora age—that is, at the beginning of His eleventh year, the luster of His body becomes so bright that it becomes an impetus for ecstatic love. Similarly, there are reddish borders around His eyes, and a growth of soft hairs on His body. In describing this early stage of His kaiśora age, Kundalatā, one of the residents of Vṛndāvana, said to her friend, "My dear friend, I have just seen an extraordinary beauty appearing in the person of Kṛṣṇa. His blackish bodily hue appears just like the indranīla jewel. There are reddish signs on His eyes, and small soft hairs are coming out on His body. The appearance of these symptoms has made Him extraordinarily beautiful."