Vipin Kumar, a paediatrician who examined Abhishek, said the balance of hormones in his endocrine glands was not normal.

The endocrine glands secrete hormones that regulate body functions like metabolism, growth and development, and reproduction.

"The sex hormone that is usually produced by the body around the age of 18 years is already being secreted in his body," said the doctor.

While Abhishek's physically growth is like that of an adult, his mental development remains that of a child.

"He is like other children of his age. He pronounces many words like a child and does other things like children," his father said.

Abhishek was first admitted to the Indira Gandhi Institute of Medical Sciences here for treatment on the advice of doctors. But after months of expensive treatment, he was taken home.

"There was no benefit despite the costly treatment," said Kumar.

Early this week, Abhishek was brought to Sadar hospital in Begusarai for a check up.

"At first, doctors were surprised to know that he was less than six-years-old as he appeared to be an adult. A three-member medical board examined him," said Gopal Mishra, one of doctors who carried out Abhishek's check-up.

His medical report will be submitted to the hospital this week after some tests.