What is the position regarding retirement during a fixed-term contract?
I am not sure that I understand what you mean by “retirement during a fixed-term contract”. If there is a fixed-term to an employment contract, there is no retirement other than the termination of the contract when it comes to an end. There is no law that says someone has to retire at a given age, 55, 60, 65 or 70 in Trinidad and Tobago. You can continue to work as long as you are able and as long as someone wants to employ you or you want to work for yourself as a contractor or a consultant.
If you have been contributing to the NIS, you stop contributing and start to receive a NIS pension at age 60.
If what you are referring to is serving on a series of fixed-term contracts for an organisation that has a retirement policy stating that retirement age is fixed at 60, or 65, then it is up to the organisation to decide whether to extend your contract beyond the date that applies to permanent employees.
Fixed-term contract employees do not normally qualify for a company pension so it is up to the person being contracted and the organisation that contracts to agree the termination date.