Why not get a subscription for online brain games? Simply put, online brain games have never been shown to prevent, delay, or treat age-associated cognitive decline or dementia. In a major study, the ACTIVE study (2002), sedentary subjects who played online brain games only improved at playing the online brain games. These skills did not transfer to any increased capability in daily living.
In 2014, one major brain game company had to settle a lawsuit from the Federal Trade Commission for two million dollars for misleading claims that their games could protect against cognitive impairment and improve performance on everyday tasks, as well as ADHD and a host of other unproven claims. See the press release from the FTC here. Sitting and playing sedentary video games will make you better at sitting and playing video games.