ato nivartatam esa
nirbandhas tava nisphalah
yatisyati bhavan kale
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
For this reason, my dear boy, you should not endeavor for this; it will not be successful. It is better that you go home. When you are grown up, by the mercy of the Lord you will get a chance for these mystic performances. At that time you may execute this function.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Generally, a thoroughly trained person takes to spiritual perfection at the end of his life. According to the Vedic system, therefore, life is divided into four stages. In the beginning, one becomes a brahmacari, a student who studies Vedic knowledge under the authoritative guidance of a spiritual master. He then becomes a householder and executes household duties according to the Vedic process. Then the householder becomes a vanaprastha, and gradually, when he is mature, he renounces household life and vanaprastha life also and takes to sannyasa, completely devoting himself to devotional service.
Generally, people think that childhood is meant for enjoying life by engaging oneself in sports and play, youth is meant for enjoying the company of young girls, and when one becomes old, at the time of death, then he may try to execute devotional service or a mystic yoga process. But this conclusion is not for devotees who are actually serious. The great sage Narada is instructing Dhruva Maharaja just to test him. Actually, the direct order is that from any point of life one should begin rendering devotional service. But it is the duty of the spiritual master to test the disciple to see how seriously he desires to execute devotional service. Then he may be initiated.