If you’re not yet aware, the brain goes through so much change early in life that it’s constantly purging, even into adulthood, to maintain optimum efficiency - Think: Use It or Lose It. Of course, the rate of this changes, depending on frequency of use, as well as stage in life. Science seems to have recently found support for this, so it was refreshing (as well as ALARMING) to see natgeo’s recent article about the teenage brain and how it undergoes a big purge during the teenage years (read it here: http://ngm.nationalgeographic.com/2011/10/teenage-brains/dobbs-text). What does this mean? It means that, as parents, we’re in this for the loooooong haul! lol … for those of you who were great at something before, stopped using it, and find yourself severely (s)lacking in skill, you’ll understand firsthand what i mean. 
anyway, i came across this post on youtube while watching a video (http://www.youtube.com/watch?v=DMStlPvcgL4&feature=player_embedded#!) and i noticed a comment, which reminded me of all this, so i’m sharing 
Here’s the Comment:
Good for his age! ;D
I’m 18 years old, stopped trainind SOROBAN with 15 years old and I was at DAN 5º… I could do easily that three digits sum count, but now I can only two digit ou three slow… 3 Years stopped got me “noob” at this
2006goto 2 years ago