Welcome back Anna! Disney Cruise Line offers all sorts of
specials offers throughout the year, so it's possible that something like that could come up. In looking at the current specials, I don't see a senior special. But, keep your eye on Disney Cruise Line's website, as the promotions change frequently.
I did a little research with AARP, and found that they are currently offering a special onboard credit for Disney Cruise Line vacations if you book through them. The credit varies from $50 up to $500, depending on the type of stateroom you book. Take a look at the AARP Travel Center website, which is run by Expedia. You'll see a cruise tab on there to click. Then, scroll down under Deals and choose Disney Cruise Line, where you can view the options for this current promotion.
Alternately, booking your Disney cruise through a travel agency that specializes in Disney sometimes offers it's own onboard credits or other booking incentives, so check out some of those options, Anna.
I hope those details help. Please do stop back again if you have other questions as you begin planning your magical sailing with Disney! I'm happy to help!