My 78 year old mum cycles three or four times a week - she goes at her own pace, and she avoids windy days because it tires her too much (she has diabetes and an unrelated 'blood condition' both of which can make her run out of energy very suddenly). I'd definitely say that traffic free would be a great choice to start with. Do you still have a bike? If not, or if you're looking to get a newer one, you might want to consider a 'step through' style. It makes getting onto the bike much easier as hips and other joints begin to lose flexibility.
All the best to you, and let us know how you get on!