Royal Caribbean or Norwegian Sky cruise.
I would look at cruise lines that cater to senior citizen. The first one I would look into is carnival cruise, just for the sheer fact they have the most number of cruises per year than any other U.S. cruise service.
http://www.cruisecenter.com/senior-cruise-specials.asp has cruise vacations for seniors. Check it out and they will hook you up with the best deals for you.
Carnival Cruise lines does offer a Senior discount. www.cruisesandseniors.com has a list of the most senior friendly cruises and it also helps you to find the best prices on senior cruises. Cruisesandseniors.com also offers information to help senior travelers find the best cruise for their needs.
Go to carnival cruise. They give early discount for booking in advance, senior discounts and all kinds of things to do. carnival.com Its always a good idea to go to a travel agent to.
There are many cruise lines that offer senior only cruises, so check with the major cruise lines to see if they offer these types of cruises. Again aarp.com offers one stop shopping for their members. They have a list of senior discounted cruises.
Many cruise lines offer great deals for seniors. It is important to shop around for the best rates. Some examples you can find online are www.cruisecheap.com/cruises/senior-discounts.html and www.vacationstogo.com/senior_discounts.cfm
There are so many different ways to book a cruise to get a great deal on it. If you don't have a travel agent, you can book online. One website to book your cruise through is vacationstogo.com.
There are hundreds of magnificent senior cruises around the world. You should consider checking out this website for all you need to know about great cruises for senior citizens. cruises.about.com/od/seniorcruises/Cruises_for_Senior_Citizens.htm
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
The best way to get a cheap cruise rate is to bundle and to watch for major discount rates. Many cruises will offer promotional discounts as well as senior discounts. I would recommend seeing: http://www.mustcruise.com/cruise_info/seniors.html.
The company Carnival is one of the best cruise companies in regards to offering senior discounts. You can visit them on the website CarnicalCruise.com.
I would suggest trying to look at some travel sites such as Travelocity, Priceline, expedia or go directly to the cruise line sites such as Royal Caribbean, Princess, Norwegian, or Carnival.