Most Institutions will issue an appointment letter stating a 5-year term, with extension subject to review. The nature of this review varies widely, being stringent and similar to the US tenure track system is a few places, to being basically a promotion review (but not a tenure review per se) in most others. That these latter Institutions, you won't lose your job but your promotion may get delayed if you haven't met the requirements (ASK what these are- varies widely). Therefore, appointments are pretty much tenured from the start with the exception of the few Institutions that have implemented or are actively discussing the implementation of a stringent tenure track system. This is something to explicitly ask, not assume, since it is a point of active debate all over the country.
Minimum: usually a few years of post-doctoral experience are required. Some Institutions have positions suited for fresh PhD applicants also eg IITs, IISER Pune, NCBS's young investigator program. Each Institution has rules to consider applicants with different numbers of post-PhD experience. Naturally, publications, proposed research plan, and references are part of the requirements and go into evaluating the application.
Maximum: there is no limit to the experience a candidate may have, but with increasing years of post-PhD experience, candidates must be considered for correspondingly higher appointments. As an example, if an Institution's rules are that 10 years post PhD experience corresponds to an Associate Professor designation, such an applicant cannot be considered for a more junior appointment. These appointments have a higher bar, and naturally require more of a demonstration of success than the promise of it as is the case with more junior appointments in which "potential" is a big factor.
Age limits: There are several institutes that prefer to hire younger people-this varies quite a lot from Institution to Institution. Age limits are usually flexible- and need to be increasingly more so in order to encourage recruitment. Make your first contact early, approx. 2-3 years before you expect to finish your postdoc. Then you will be in touch with the changing situation at various places.
This is a companion discussion topic for the original entry at https://indiabioscience.org/faqs/jobs-in-india