Your post is a bit confusing since you do not tell us which port. It is unlikely that you are actually going to Nice since you could walk from ship through town. If you are tendering into Villefrance, that port is only about 12 min from Nice via train or a bit longer if you grab the public bus. If you are tendering into Cannes, than it does take about 45 min to get to Cannes via the train. There are both trains and regional buses that span the Riviera coast, but we would have some concern about doing this with an 82 year old. You also need to consider why you want to go to Nice? Do you have a specific destination such as the old town area, the Promanade, museums, etc.