Part of what I'm doing now leading up to my concert with the Colonial Symphony on October 23rd, is to prepare to conduct three pieces from memory - Stravinsky's 1919 Firebird, Falla's Three Cornered Hat Suite No. 2, and Rimsky-Korsakov's Capriccio Espagnol.
I think that memorizing music becomes easier as one gets older, which is counter intuitive in many ways. People always comment to me about how they seem to be having an increasingly difficult time remembering things from their past. On one level I think that is true, but on another, I think memory is related strictly to effort.
Here's what I mean: I think my musical memory has gotten sharper because I have a more profound love for music and appreciation of its depth. When I have a love for something such as a great score, I seem to look at it with different eyes - ones that cherish the moments I have in its presence. My time is more limited in study than it once was because of my family commitments and because of the steep administrative load I have (see the blog below!), but I work faster now and more intensely, and also with greater affection and appreciation. When I apply an honest passion, it becomes much easier to remember even small details of a massive work, and when that music is in my head and bones, it tends to sing me with greater precision and presence.
I think most of colleagues who have passed the 40 threshold would agree that they are much faster to digest material now - no matter if it is musical or not. The specificity with which they remember however, is related to the intensity and passion which they inject into their study, and in when applied with passion, the ability to remember seems to me to increase with age - no matter how old or young you are!