Compared to "Big Brain Academy", "Brain Age" seems geared towards a slightly older audience. It's less cutesy, and seems more scientific, although it's not as much fun.
Basically, you get to measure your brain age, and complete practice exercises. What's different about this title is that only your first attempt per day is recorded for the books. You can repeat the exercises and test if you want, but it won't count until a different day. I guess this works better since the game is trying to track progress on a daily basis (rather than have people redo certain exercises over and over, trying to get the best scores in everything all at once).
Also, you only start out with a handful of exercises, but more are unlocked as you play longer and get more "stamps".
It all works well, but don't expect to be entertained all that much. The microphone seems to work pretty well, but it's obviously not perfect. When you verbalize "blue", "black", "red", or "yellow", they are rarely mixed up.
The stylus writing is a bit more problematic, so you have to get used to certain things. For instance, I tend to write the number "5" with the vertical line on down, drawing in the top line last. In "Brain Age", it will prematurely interpret my writing as a "7". The best way to remedy this is to write your "5"s like an "S".
Overall, a pretty good title to keep sharp. Not really recommended for the younger audience though.