Dear Kumar,
Age of retirement on superannuation prescribed in the model standing orders under the IE(SO)Act,1946 is a guide line only. As such, an employer can determine a higher or lower age for superannuation for his employees in the establishment depending upon the nature of their work. But, it is always better to stick to the age as fixed in the standing orders in order to have effective succession and fairness in matters of promotion and uniformity of tenure of employment. However, in extraordinary circumstances like the necessity of completion of any special project which requires the specialised knowledge of the retiring employee or non-availability of suitable replacement from within the organization or from outside etc., the retiree's services may be extended accordingly for some more time or retain him as a consultant on retainer basis. This is the practice followed for high-profile positions in the organization.
In case of lower category employees like helper, above such practice is not generally advisable for it may lead to favoritism or bias. But the employer is the ultimate judge - he can extend the tenure as he deems fit and no legal restrictions.