Odd question, but do you read as much literature as when you were young? There seems to be a fairly strong correlation between reading literature/fiction and concentration in studies (and no, I don't have the sources on hand, I heard mention of them on YouTube, of all places.. Boo, I know. Improper citation, but what are you gonna do. Sometimes I listen to lectures when I work). I, personally, had gotten into the habit of reading technical papers all of the time and foregoing literature and fiction on the basis of "well, what good is that doing me?!" and had noticed that my focus had been slipping. Now, this could be anecdotal or I could have just needed the down time but, I started reading some scifi (is that what Hitchhiker's Guide and John Dies is?) again and my concentration seems to have gotten slowly better.... could also just be time away from the screen. Though I do read on a Kindle Paperwhite, so who knows.