There's a long list of activities that have been shown to slow or mask cognitive decline in the elderly, e.g. reading, being bilingual, learning a second/foreign language, and physical exercise but most of all, social engagement. There have been a number of studies that have shown remarkable improvements in not only cognitive function but also quality of life in retirement homes where they've enacted programmes where small children visit. The residents talk to the children, read them stories, and various other activities. Also beats crappy day-care where the carers barely have enough time to feed and change the children in their care, let alone engage with them socially and play with them.