Could you ride a cruiser style bike? You sit pretty much upright in those.
No they aren't going to be good for long rides but you could still get out. There's an older fellow that rides one around here
Speaking of long rides (for me). I did 63.6 miles today just 0.2 miles short of my longest ride. It wasn't very hilly, only about 2930' of climbing but I felt pretty great at the end of it (except for my right foot that was killing me at the end, the bike shoes are just a bit too tight for my wide feet). My speed was very good for the distance I thought, 15.8 mph. It's the second time I did a metric century. Never going to be a big long distance rider but I was pleased with how good I feel afterwards