Dear Mohamad Rafiq
Let me see if I understood your statement :
Do you mean to say that on the bio-dta form filled on Jan. 2004, his age was shown as 40 years on that date ?? (and not 40 years, when he joined in Jan 2004).
What it implies is, as on 2010 he is only 46 years old and hence years away from retirement.
What should have been done in this case was, to have a Medical Examination in 2004 (when this matter came to light); and asking the Doctor to estimate the age; which is considered as valid. In case of any protests/dispute, the employee should submit certain documents relating to age like certificate from "gram panchayat", records from primary school, any court document relating to age etc.
You can subject the employee to a Medical examination, even now, and get a medical estimate of his age; and act accordingly.
However, do remember, to give the employee the benefit of the lower side of the range of the estimated age.
Warm regards.