krame bālya-paugaṇḍa-kaiśoratā-prāpti
rāsa-ādi līlā kare, kaiśore nitya-sthiti
krame - gradually; bālya - childhood; paugaṇḍa - boyhood; kaiśoratā - youth; prāpti - development; rāsa - dancing with the gopīs; ādi - and others; līlā - pastimes; kare - performs; kaiśore - in His age of pre-youth; nitya-sthiti - eternally existing.
The comparison made here is very interesting. Kṛṣṇa does not grow like an ordinary human being, even though He exhibits His pastimes of childhood, boyhood and pre-youth. When He reaches the age of pre-youth, kaiśora, He does not grow any older. He simply remains in His kaiśora age. He is therefore described in the Brahma-saṁhitā (5.33) as nava-yauvana:
advaitam acyutam anādim ananta-rūpam
ādyaṁ purāṇa-puruṣaṁ nava-yauvanaṁ ca
vedeṣu durlabham adurlabham ātma-bhaktau
govindam ādi-puruṣaṁ tam ahaṁ bhajāmi
This nava-yauvana, or pre-youth, is the eternal transcendental form of Kṛṣṇa. Kṛṣṇa never grows older than nava-yauvana.