Bardolino would be fine, its a fairly flat town with just a very slight incline to reach the main road. The lakeside and most of the town centre is flat, nice wide paved streets and traffic free. There are ramps onto the ferries and the staff are always on hand to give any assistance. There are quite a few hotels right on the lakeside.
Travelling around the lake you should be okay in most of the towns, Lazise, Peschiera del Garda, Torri del Benaco, Riva del Garda, Salo etc. Sirmione is fairly flat but the streets are quite narrow and do get very busy, so maybe not ideal for walking. The main one to avoid would be Malcesine which has a small lakeside area but steep cobbled streets. Limione also has steep cobbled streets but has a nice flat lakeside promenade.Edited: 10 July 2018, 15:32
Garda has a long, flat lakefront promenade and also has several lakefront hotels which lead directly to the promenade.
The path between Bardolino and Garda is wide and traffic-free, and there are benches at regular intervals.
Bardolino would be perfect for you, We met a lovely older lady and her husband who was in a wheelchair and they were having no problems getting around, i think because it is quite flat and easy for walking a lot of older people choose it. Neighbouring Garda and Lazise are also flat. If you stay central everything is basically on your doorstep and you don’t have to walk too far with plenty of cafes to have a seat and watch the world go by. Definitely go, you won’t regret it! ☀️😎