This website http://seniortravel.about.com/od/cruises/Senior_Travel_Cruises.htm has a lot of information about cruises and specifically for seniors. It also has links on the website to re-direct you to book a cruise after reading all the information. All general questions can be answered on this website.
You can find information on single senior cruises for your grandmother by seeking travel agents who specialize in senior vacation packages. Very few general travel agents or online booking sites offer this service.
Many travel agencies offer cruises that are aimed towards seniors. For some examples online you can visit www.americandiscountcruises.com/senior-citizen-travel.html
A lot of information is available on the web regarding senior travel clubs. One place that you will find helpful is at www.suddenlysenior.com/TRAVELPAGE.html
Many cruise offering companies provide senior discounts. Here are some senior discounts from Carnival Cruises: http://www.cruiseone.com/travel/editorial.jsp/edType/Custom Page/pagename/Carnival_Senior_Specials?. Also, here is some more information on senior discounts for cruises: http://www.cruisecheap.com/cruises/senior-discounts.html
Carnival Imagination cruises are available to the Bahamas, the Caribbean, Mexico and the Panama Canal. One can find detailed information about cruises on the Carnival website or by visiting a travel agency.
There are many agencies which organize special Costa Atlantica Cruises. One can visit Costa Cruises site to find out more information regarding specials on Costa Cruises.
Many mature travelers enjoy cruise vacations. By searching the web and online forums you can find a lot of information and recommendation on cruises that are of interest to you. One site is cruisecritic.com and seniortravel.about.com.
Senior citizens get discounts on many cruiselines. Travel agencies also have specific discounts for senior citizens looking to cruise.
There are several cruise lines that hold senior cruises and offer discounted rates. To compare prices, check out http://www.mustcruise.com/cruise_info/seniors.html, or http://odysseys-unlimited-catalog.com/Senior Travel Cruises.html?gclid=CMPUjqb7_qkCFUTBKgodCWNAxw
Information for cheap Carnival Cruises can be found by visiting online sites and comparing prices. Other places that can offer cheap deals can include newspapers, magazines and local travel agents.
Many cruise lines cater to senior citizens. HAL, Costa and Celebrity are a few. You can find all the information you need here: http://seniors-site.com/travel/cruises.html
Visit their website. There is a lot of information about their cruises, pictures from past cruises, and prices for upcoming cruises. Also, read reviews from different travel magazines.