A Reduced Fare MetroCard is the ticket for tourists or travelers 65 or older who want to save big bucks on transportation throughout the New York City region, starting from anywhere.
What’s more, travelers can use the card everywhere in the region on Metropolitan Transit Authority buses, trains and subways. Regular subway or bus fare is $2 per person but $1 for senior citizens per ride. Large discounts are also available on Long Island Railroad commuter trains and Metro North trains to nearby suburbs.
The key is applying for the card at least a month in advance. Age and a valid I.D. are the only requirements, regardless of a visitor’s permanent home town !!!
Step by Step - Getting A Reduced Fare MetroCard
Print out an application from the MTA website.
Obtain a passport sized photo of yourself
Have a notary public stamp the application in the space provided.
Charge the first $10 on a credit or debit card or enclose a check or money order.
Mail application and photo with a Xerox or photocopy of a driver’s license or other proof of age that includes your picture to the address provided..
Applicants typically receive the card within one month, and can use it immediately upon arrival in the City.

Those who don’t want the hassle of applying in advance for a Reduced Fare MetroCard can get one easily (with photo I.D. or driver’s license) at the Walk In Center in lower Manhattan, without a notary. They will take your picture and help you fill out the form.
(copied from MTA Web site, and I have one, living in Maine, visiting the City twice a year, card good for 2yrs)