nasmatto yuvayos tata
putrabhyam abhavan kvacit
[Lord Krsna said:] Dear Father, because of Us, your two sons, you and mother Devaki always remained in anxiety and could never enjoy Our childhood, boyhood or youth.
Srila Visvanatha Cakravarti discusses this verse as follows: “One may object that at this point Lord Krsna had not actually passed the kaisora stage [age ten to fifteen], since the women of Mathura had stated, kva cati-sukumarangau kisorau napta-yauvanau: ‘Krsna and Balarama have very tender limbs, being still at the kisora stage, not having reached adolescence.’ (Bhag. 10.44.8) The definition of the different stages of growing up is given as follows:
yauvanam tu tatah param
‘The kaumara stage lasts until the age of five, pauganda up to age ten and kaisora to age fifteen. From then on, one is known as yauvana.’ According to this statement, the kaisora period ends at the age of fifteen. Krsna was only eleven years old when He killed Kamsa, according to Uddhava’s words: ekadasa-samas tatra gudharcih sa-balo ’vasat. ‘Like a covered flame, Lord Krsna remained there incognito with Balarama for eleven years.’ (Bhag. 3.2.26) And since Krsna and Balarama never took brahminical initiation in Vraja-bhumi, it was at the time [of Their going to Mathura] that Their kaisora stage began rather than ended.
“This objection to Lord Krsna’s statement in the present verse — that His parents could not enjoy His kaisora stage — is based on ordinary measurement of age. Yet we should consider the following statement:
ramah krsnas ca go-vraje
‘O King Pariksit, within a short time Rama and Krsna began to walk very easily in Gokula on Their legs, by Their own strength, without the need to crawl.’ Sometimes we see that the son of a king, even while in his pauganda stage of life, undergoes exceptional physical growth and exhibits activities appropriate to a kaisora. Then what to speak of Lord Krsna, whose exceptional growth is established in the Vaisnava-tosani, Bhakti-rasamrta-sindhu, Ananda-vrndavana-campu and other works?
“The three years and four months that Lord Krsna stayed in Mahavana were the equivalent of five years for an ordinary child, and thus in that period He completed His kaumara stage of childhood. The period from then to the age of six years and eight months, during which He lived in Vrndavana, constitutes His pauganda stage. And the period from the age of six years and eight months through His tenth year, during which time He lived in Nandisvara [Nandagrama], constitutes His kaisora stage. Then, at the age of ten years and seven months, on the eleventh lunar day of the dark fortnight of the month of Caitra, He went to Mathura, and on the fourteenth day thereafter He killed Kamsa. Thus He completed His kaisora period at age ten, and He eternally remains at that age. In other words, we should understand that from this point on the Lord remains forever a kisora.”
Thus Srila Visvanatha Cakravarti analyzes the intricacies of this verse.