Some good suggestions above.

I pretty much concur with the wee drummer's recommendations re gigging in senior citizen facilities. I've been supporting myself primarily via doing such gigs for 13 years and could have made considerably more at it if I'd gotten better organized a few years earlier.

Bear in mind that not all "old folks" facilities are nursing homes. There are independent living and assisted living facilities with mentally and/or physically high-functioning seniors, with broad musical tastes, as well as drop-in senior (social and activity) centers that cater to people from their 50s on up, many of whom are not retired.   

Drummer's right, it's not a quick fix if you want to develop a steady clientele.   You'll probably need to expand your repertoire and maybe acquire some versatile and portable sound equipment to meet various needs (such as playing in large dining rooms with people spread out all over the room, and trying to entertain audiences with mixed tastes in music).

I don't think the "senior circuit" will work unless you're in a good sized metropolitan area that you can get around in fairly quickly by car.   

The Fender PassPort PA system is good for large rooms, parties, dances, etc., and I like the tip about directing your speakers at the wall.   (Inevitably, when I have a speaker in a dining room, the person with the most sensitive ears and/or the most distaste for music will sit directly in front of the speaker. It's a law of nature.)

I find my Fender Amp Can - small wireless PA unit the size of a 3-lb coffee can -- just right for smaller gigs, such as sing-alongs in small dining rooms. A lot easier to set up than the PassPort, cutting the total time down to where I can afford to do some gigs for about $40 to $50 and still make it profitable.

I also find a wireless system with a lavaliere mic helps me "work the crowd," especially in facilities where part of my job is to get the residents singing along, dancing, clapping along.

I agree about the lightweight clothes.   The residents may not all want the temp 75º to 80º but way too often the STAFF seem to assume that it's some sort of elder abuse to keep the temp around 72º and have residents wear sweaters in January if they feel cold. But I digress.
My recommendation is to dress in layers.   I usually wear tank tops, but every once in a while I'll find the temp at a more normal setting.

I haven't yet started working with backing tracks, though I have a couple small Karaoke machines that I use as amplifiers.    But I have developed a large repertoire of classic country, show tunes, trad jazz tunes, and Tin Pan Alley tunes, plus selected frequently requested pop songs from the 50s, 60s, and 70s to complement my folk, international and Gospel repertoire.    It doesn't take too long to get a feel for the songs and genres with the widest appeal.

This point by wee drummer is key, in nursing home settings:   [[Walk round sing to them individually. shake hands, make contact. Smile - sometimes it's the friendliest face they will see all week. And be cheerful, you are doing a job you love - if you don't love performing - I can't imagine how soul destroying it might be. some people are very ill and can scarcely respond, but its brilliant when they do. beats anything! ]]
I am more in demand as a performer for the retirement home circuit than some people with better voices and better instrumental skills, simply because I'm a ham, I involve and energize my audiences, and I tailor my programs to suit those audiences -- partly by having a huge, eclectic repertoire and finding out what kinds of songs they appreciate.
(Usually it's things they've heard before, but not always.)

I agree, "ordinary folk songs" don't go over well, but I do get good response a lot of the time to the popularized folk music of the Weavers, KT, PP&M, Carter Family, etc. And in theme programs (e.g., "Around The World" or a St Pat's Program) I can throw in a folk song or two that they haven't heard and most will appreciate it.