What is the yearly rate of incremental premium increases for health insurance policies in India? Is there any upper or lower limit of increase?

Mostly it increases based on:

Taxes.

Age - after a age of say for eg: every 3 or 5 years based on insurance companies premium raises.

Otherwise premium will not increase for existing customers due to increase in medical costs.

Say at age of 20 if u brought a policy in 2017, you would have paid a premium of 10,000.

But if I brought a same policy at the age of 20 in 2025, i would be paying higher premium as costs would have been increased.

There is no way to calculate the exact percentage or predictable range. As you see the factors are all highly variable.