Hi Tony,
I have played Senior Venus for about 7 years now and what I find is just about any of the popular hits from about 1920 - 1960 works really well. Just think of all the famous singers, big bands, movie songs, broadway show songs from these eras and you have it made.
Another finding - if I play at a certain place say twice or three times a year you can just about play the same songs because they just don't remember. I have had people ask me if I had been there before at places I play monthly!
I currently have a book of about 2000 songs that I can play if I get requests - which is rare because many of the "Seniors" don't remember the titles of the songs. They often ask for a song by reciting a lyric from the song.
Another thought, I played with a dozen or so Big Bands through the years and each of them had a book of about 100 songs that we played over and over at every gig. For us it got really boring but the audiences loved it because we were playing familiar songs they came to hear.
Your choices for songs is almost endless and I think that is what makes the senior gigs a joy. I have always been surprised at how many of them remember the melody to songs I play and often say it has been years since they have heard that song.
The real challenge for arranger players like us is to get all the songs setup on the instrument. That takes a lot of time but once done is worth the effort.
Anyway, good luck with the adventure and let us know how it goes.
Deane