I'm not thoroughly sold on the "too old to learn" adage either. I think it has more to do with time and focus. Since moving into the stage of life in which I have a family and more responsibility in my job, I have considerably less time to focus on learning a new instrument or music theory or ______.

I have no doubt that there is an age, beyond which, your brain has degenerated too much to learn. But, I'm not convinced it's as early as 50's or 60's. Hopefully, with better awareness about nutrition, exercise, and stress, we can see people learning music instruments well into their 80's.