First, I agree with Donna; contact a good cruise specialist who has been there done that so they can advise you accordingly.
Second, personally I think Holland America is the best for providing cruises and cruise/tours for the older crowd. We did a 2 week cruise tour with them and it was awesome!
Third, I disagree with others about the balcony cabin. Personally, I would rather save the money on my cabin and spend more money on excursions, because Alaska is definitely one of those places you want to do some excursions.
Let me know if you have any questions.