Exercise bike workout for a 75 year old?

I'm 75 and have osteoarthritis. I'm trying to keep fit by walking every day, but have decided to make use of a stationary bike I haven't used it in years, but it makes a good clothes horse! However, I don't want to overdo it, just exercise enough to keep mobile and active.

Can anybody suggest an easy daily workout I could follow? Can't seem to find much online.