Krsna never ages beyond youth

Expressions researched:
"never ages beyond youth"

BG Chapters 1 - 6

But astonishingly enough He never ages beyond youth.

BG 4.6, Purport: The Lord, however, does not do so. Whenever He appears, He does so in the same original body, by His internal potency. In other words, Kṛṣṇa appears in this material world in His original eternal form, with two hands, holding a flute. He appears exactly in His eternal body, uncontaminated by this material world. Although He appears in the same transcendental body and is Lord of the universe, it still appears that He takes His birth like an ordinary living entity. And although His body does not deteriorate like a material body, it still appears that Lord Kṛṣṇa grows from childhood to boyhood and from boyhood to youth. But astonishingly enough He never ages beyond youth. At the time of the Battle of Kurukṣetra, He had many grandchildren at home; or, in other words, He had sufficiently aged by material calculations. Still He looked just like a young man twenty or twenty-five years old. We never see a picture of Kṛṣṇa in old age because He never grows old like us, although He is the oldest person in the whole creation—past, present, and future. Neither His body nor His intelligence ever deteriorates or changes. Therefore, it is clear that in spite of His being in the material world, He is the same unborn, eternal form of bliss and knowledge, changeless in His transcendental body and intelligence.

Bhagavad-gita As It Is Lectures

Similarly, Kṛṣṇa's līlā, Kṛṣṇa's pastime, is going on. Everything is going on at the same moment. Therefore His līlā is called nitya-līlā. Nitya means eternal. It does not change.

Lecture on BG 4.6 -- Bombay, March 26, 1974:

Pradyumna: "Although He appears in the same transcendental body and is Lord of the universe, it still appears that He takes His birth like an ordinary living entity. Despite the fact Lord Kṛṣṇa grows from childhood to boyhood, and from boyhood to youth, astonishingly enough, He never ages beyond youth. At the time of the Battle of Kurukṣetra, He had many grandchildren at home, or, in other words, He had sufficiently aged by material calculations. Still, He looked just like a young man, twenty or twenty-five years old. We never see a picture of Kṛṣṇa in old age because He never grows old like us, although He is the oldest person in the whole creation, past, present and future. Neither His body nor His intelligence ever deteriorates or changes. Therefore it is clear that in spite of His being in this material world, He is the same unborn eternal form of bliss and knowledge, changeless in His transcendental body and intelligence. Factually, His appearance and disappearance are like the sun's rising, moving before us and then disappearing from our eyesight. When the sun is out of sight, we think that the sun has set, and when the sun is before our eyes, we think that the sun is on the horizon."

Prabhupāda: Kṛṣṇa does not appear or disappear. Our eyesight changes. Just like we are looking through the window. One horse race is going on. When the horse comes before the window, we can see. And when it passes through, from our eyesight, we think that horse is no longer existing. But the horse is running. This example should be taken. Kṛṣṇa is called nitya-līlā. He is taking His birth, He is fighting in the battle of Kurukṣetra, He's dancing with the gopīs. That is going on eternally in either of the so many, innumerable universes. So the same time...

Just like the change of time. Now it is nine o'clock in the watch. Now, this nine o'clock, this is now night. The morning nine o'clock is still existing somewhere. Similarly, Kṛṣṇa's līlā, Kṛṣṇa's pastime, is going on. Everything is going on at the same moment. Therefore His līlā is called nitya-līlā. Nitya means eternal. It does not change. Go on.

1973 Conversations and Morning Walks

Purāṇa-puruṣa, the oldest man, oldest living entity, but nava-yauvana, just like young man.

Room Conversation with Sir Alistair Hardy -- July 21, 1973, London:

Pradyumna: "The Lord has spoken about the peculiarity of His birth. Although He may appear like an ordinary person, He remembers everything of His many, many past births, whereas a common man cannot remember what he has done even a few hours before. If someone is asked what he did exactly at the same time one day earlier, it would be very difficult for a common man to answer immediately. He would surely have to dredge his memory to recall what he was doing exactly at the same time one day before. And yet, men often dare claim to be God, or Kṛṣṇa. One should not be misled by such meaningless claims. Then again, the Lord explains His prakṛti, or His form. Prakṛti means nature, as well as svarūpa, or one's own form. The Lord says that He appears in His own body. He does not change His body as the common living entity changes from one body to another. The conditioned soul may have one kind of body in the present birth, but yet a different body in the next birth. In the material world, the living entity has no fixed body, but transmigrates from one body to another. The Lord, however, does not do so. Whenever He appears, He does so in the same original body by His internal potency. In other words, Kṛṣṇa appears in this material world in his original eternal form with two hands, holding a flute. He appears exactly in His eternal body, uncontaminated by this material world. Although He appears in the same transcendental body and is the Lord of the universe, it still appears that He takes His birth like an ordinary living entity. Despite the fact Lord Kṛṣṇa grows from childhood to boyhood and from boyhood to youth, astonishingly enough, He never ages beyond youth. At the time of the Battle of Kurukṣetra, He had many grandchildren at home, or in other words, He had sufficiently aged by material calculations. Still, He looked just like a young man, twenty or twenty-five years old. We never see a picture of Kṛṣṇa in old age because He never grows old like us, although He is the oldest person in the..."

Prabhupāda: Advaitam acyutam anādim ananta-rūpam ādyaṁ purāṇa-puruṣaṁ nava-yauvanaṁ ca [Bs. 5.33]. Purāṇa-puruṣa, the oldest man, oldest living entity, but nava-yauvana, just like young man. Nava-yauvanaṁ ca. Advaitam acyutam anādim ananta-rūpam ādyaṁ purāṇa-puruṣam [Bs. 5.33]. Purāṇa means oldest, because He's the origin of all living entities. But nava-yauvanaṁ ca, just a fresh, young man. Hm. Go on.