As long as you are physically able, there is no reason not to start today. Being an arthritis suffer and now at age 58, I know how difficult it is make those old fingers do what you want and when you want it. But like you said, you aren't looking to be a professional; you just want to have some fun. Doc Waston is 85 and Charlie Daniels (guitar & fiddle) is 71. Like many of the older pros they are still playing and entertaining.
I know how it is, always dreaming about doing something and never doing it. There is always some reason not to. Usually it is to provide for someone else. Well, you are all out of reasons. There is no reason for you not to start playing today. Heck, you can learn a few chords within the hour!
Good luck! Just start and keep it up. Remember we are all pulling for you. Let's hear you play "Jingle Bell Rock" by CHRISTmas. The tabs and lyrics are available on the web.
GB!