Denver continually makes the tops of charts for "best cities to live in." This is widely due to its active/liberal culture, its fantastic weather, and wonderful scenery. It is known as the Mile High City, because of its elevation: 5,200 feet (1 mile) above sea level. High elevation is very helpful for seniors. It helps them breath easier, once they get accommodated to it, and the arid air makes for more comfortable temperatures. Since Denver is coming out of a giant housing boom, there are tons of new assisted living facilities and retirement/active-55 communities throughout the city. There is also a well-established home health industry to keep you living semi-independently, if that is what you want.
Denver is a great city for children, as well. There are plenty of things to do in Denver with the grandchildren. Even if you have mobility restrictions, there are plenty of wheelchair accessible sites around Denver.
The closeness of the mountains has made Denver a popular residence for active people. Skiing is popular in the winter, and day-trips up to the quaint mountain towns happen during the summer. Within the city limits, neighborhoods along downtown's perimeter are getting hipper and trendier, with better cuisine and social activities. Denver has over 200 parks, making it one of the few cities where you can thoroughly explore on a tight budget. There are playhouses, concerts, and a world famous new modern art museum. For major league sports there are the Denver Broncos for football, the Colorado Rockies for baseball, the Colorado Avalanche for hockey, and even a professional soccer and rugby teams. Less than an hour's drive west of the city are two gambling towns: Black Hawk and Central City. Colorado has one of the biggest craft beer cultures, as well as Coors and Budweiser factories. The city's transportation options are ever increasing, with a new light rail system currently expanding.
The city has a history of left/democratic politics, and has recently legalized marijuana for recreational use. But do not worry, for those that do not smoke, hardly a thing has changed (it is not in your face).
The sudden changes in climate can be hard to get used to, but many of the residents really enjoy having 70-degree weather for a few days in February, and late/unexpected snows. The traffic is also a small problem, but that is getting better as new options like the light rail are becoming a reality.