Amazing. For most of us, your career begins about 22 and ends about 72. So at 50 years, the midpoint would be 47. Yet most of the comments below start with, "I'm 35 and...".

Jeez. At 35 you're still just a kid.

I'm 57 and I've definitely seen brain changes. At 20 I could learn 80% of new stuff in one pass. That ended by 35, when I had to take and review notes to learn as well. Now at 57, I simply can't remember minutiae like I once could. Proper nouns are especially tough to recall (famous names especially). I don't retain entire 1000 LOC programs in my head any more.

Learning new computer languages still isn't too tough but breaking new ground in math is. My ability to see multiple perspectives of a new concept all at once is not what it once was. I have to work harder at concentrating and distractions are more disruptive. I really HATE working in an open space without earplugs.

So yes, the brain ages. At age 50 I'll be much more impressed when you claim, "Oh yeah, my brain hasen't lost a step since 20."