Our Age Doesn't Make Us Elderly - Prabhupada 1032
680612 - Lecture SB 07.06.01 - Montreal
So our childishness or experience, old age, means according to the acquirement of knowledge. If one is advanced in knowledge, he is to be understood older. And if one is not advanced in knowledge, he is a child. That's all. So child does not mean that a five-years-old boy. Just like Prahlāda Mahārāja, he was only five years old, and just see how nicely he is teaching. So he is older than any other man. At least, he is older than his atheistic father.
So you should always remember that any man who is not aware of a particular subject matter, he is a child in that subject matter. And one who is fully aware in his particular subject—it doesn't matter what is his age—he is to be considered as elderly.