Look at the rating of a game to determine if it's "Adult Software". Does Brain Age have a Teen, Mature, or Adults Only rating? Umm no, so it's not "Adult Software", in fact all the software the original poster mentioned is family friendly. Sorry but Nintendo isn't the leader in "Adult Software" and there is nothing wrong with that so original poster, please don't get upset and just enjoy all the family friendly games.
PS. When I say "Adult Software" I mean software with adult themes and aimed squarely at *gasp* adults. A game's rating is a pretty big giveaway.
Edit: Oh and incase the game's rating doesn't give it away ask yourself a question "Would Jack Thompson get angry and want to sue someone if he saw the game", if the answer is no then it's not "Adult Software".
Adults only ratings don't make a game to adult software.
Some notes about Brain Age: The game tracks your brain age only from 20 to 80. Nintendo is marketing the game as software for adults and the game doesn't track brain ages below 20. It may be a family-friendly game, kids and teens can play it, but it doesn't track their age group.
So I would say that the game becomes pretty pointless for kids and teens after a short period. Also kids and teens have to solve similar tasks that the game offers pretty much every day in school, so they are looking for different games anyway. Brain Age isn't aimed at them, it's for adults.
Nintendo stated that more than a third of the Brain Age gamers are 35+ years old. They have also stated that they shipped more than 10 million units of the first Brain Age game worldwide.