Apart from the senior citizen discount (50% for women over 58 and 40% for men over 60), most of the railway concessions aren’t available to foreigners. To get the senior citizen discount, you have to be sure to check the little box asking if you want it when you are booking. It’s not automatic, even though you do have to list your age. You have to carry your passport when you are traveling. If they ask and you don’t have it, you’ll have to pay the difference for the full fare.
You only get the discount with tickets purchased in advance, either in person or online. It’s not available at the Current Reservation counter or on the train.