Srimad Bhagavatam Canto 04, Chapter 12, Text 43

SB 4.12.43

yah ksatra-bandhur bhuvi tasyadhirudham
anv aruruksed api varsa-pugaih
sat-pañca-varso yad ahobhir alpaih
prasadya vaikuntham avapa tat-padam
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Dhruva Maharaja attained an exalted position at the age of only five or six years, after undergoing austerity for six months. Alas, a great ksatriya cannot achieve such a position even after undergoing austerities for many, many years.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Dhruva Maharaja is described herein as ksatra-bandhuh, which indicates that he was not fully trained as a ksatriya because he was only five years old; he was not a mature ksatriya. A ksatriya or brahmana has to take training. A boy born in the family of a brahmana is not immediately a brahmana; he has to take up the training and the purificatory process.
 
The great sage Narada Muni was very proud of having a devotee-disciple like Dhruva Maharaja. He had many other disciples, but he was very pleased with Dhruva Maharaja because in one lifetime, by dint of his severe penances and austerities, he had achieved Vaikuntha, which was never achieved by any other king’s son or rajarsi throughout the whole universe. There is the instance of the great King Bharata, who was also a great devotee, but he attained Vaikunthaloka in three lives. In the first life, although he executed austerities in the forest, he became a victim of too much affection for a small deer, and in his next life he had to take birth as a deer. Although he had a deer’s body, he remembered his spiritual position, but he still had to wait until the next life for perfection. In the next life he took birth as Jada Bharata. Of course, in that life he was completely freed from all material entanglement, and he attained perfection and was elevated to Vaikunthaloka. The lesson from the life of Dhruva Maharaja is that if one likes, one can attain Vaikunthaloka in one life, without waiting for many other lives. My Guru Maharaja, Sri Srimad Bhaktisiddhanta Sarasvati Gosvami Prabhupada, used to say that every one of his disciples could attain Vaikunthaloka in this life, without waiting for another life to execute devotional service. One simply has to become as serious and sincere as Dhruva Maharaja; then it is quite possible to attain Vaikunthaloka and go back home, back to Godhead, in one life.
Srimad Bhagavatam Canto 04, Chapter 12, Text 42
Srimad Bhagavatam Canto 04, Chapter 12, Text 44