The positive effects of exercise on brain health have been demonstrated in many studies now. The next step may be to develop low-cost programs in the community that provide appropriate support and structure for adults (especially older adults) to encourage physical activity.
A great example of such program is The Adult Playground in Beijing, China (Dhand et al., 2010):
Half a football field large, this space consisted of all-weather stretching and strengthening equipment such as elliptical machines, flat benches, modified leg press machines, railings at different heights, monkey bars, and arm and leg rotatory devices. The area was teeming with adults, most older than 60 years, who were not only exercising but also playing games such as Chinese hacky sack (a Chinese game from the 5th century BC) and traditional board games.
The Chinese government has erected several outdoor adult playground of this type across urban areas. This seems to be a great example of a low-cost, easily accessible, solution combining physical exercise with socialization as well as cognitive exercise.