Hello Vishwanath,
The age of retirement is not the same everywhere. It differs from central government to state government. It also varies across different sectors and employments. Companies also have their own retirement policies.
Since PF is deducted from the basic pay, it is applicable until the retiring person's last drawn salary, i.e., 12% of the last drawn basic pay.
The income tax for senior citizens, very senior citizens, and very very senior citizens is provided to offer them the benefit of tax reductions. The percentage of tax varies among different age groups, so it has no direct connection with the PF deductions.
In fact, for government employees, their pension is fixed based on their last drawn salaries. For example, if you retire in May and receive a hike in May or the previous month, the increased salary is considered for the pension amount. Therefore, the last drawn salary is always taken into account for the final settlements.
(May observe the Tax Slabs: Income tax slab 2012-2013 | financeminister.in)
The main reasons behind such tax variations are the high cost of maintenance, such as medical expenses and dependency. Additionally, the salary they used to receive when they retired was meager in India.