Re the IC card issue:
Just to let you know, Tokyo Metro and the Toei Subway offer
one-day passes that CAN be loaded onto a PASMO card (the touch and go IC cards).
A one-day pass valid on both Toei and Metro costs \900 a day, and one valid only on the Tokyo Metro costs \600.
It could definitely save you money (and hassle) if you're planning to visit more than one location on the subway. (which, as long as you're staying within the central areas, should be enough) I'd load an additional 1000 yen or so on the IC card to cover incidental purchases at convenience stores, vending machines, etc.
The passes below are separate paper tickets, and cannot be loaded on a PASMO/SUICA card.
If you anticipate travelling on the JR lines too, the
Tokyo 1-Day Ticket might suit you better, covering both the subway, Toei Bus, Streetcar, and the JR lines within central Tokyo. At 1,590 yen, it's a bit harder to recoup the cost though.
If you're travelling through NRT, the
Skyliner+Subway combination pass might be the best value.
Considering that a one-way ticket on the Skyliner (express train from Narita into Tokyo) usually costs 2465 yen, you can essentially get a 24 hour subway pass (on both Metro and Toei) for 325 yen, a 48 hour pass for 735 yen, and so on.
Unfortunately Senior discounts aren't available, but the Subway passes are eligible for
extra value "Chika Toku" promotions at various locations that you might end up visiting, which might also add towards your perception of value for each ticket.