How does the law of Rhythm work?

As a rule, those who say that they have been long here do not seem old.

I asked the Teacher why, and he said that after a time an old person forgets that he is old―that the tendency is to grow young in thought and appearance―that the body tends to take the form, which you hold of it in your mind―that the law of Rhythm works here [in the world of spirits], as elsewhere.

―The Judge