Is it possible to start out at, let’s say, 20 years and be sharp as a knife. Never forgetting things, never dropping things, always have an answer ready and can do multiple things at once. And then around 30 you suddenly drop stuff you have in your hands, you forget if you locked the door, your contactlenses have gone missing from the storagecontainer, people need to stop talking while you drive?
Oh yes, there’s many things that can cause this as others have said. Stress, sleeplessness, mental problems or illness, and especially physical health and weight. I’m almost 40 and I find I have “degraded” in many ways due mostly to my weight, depression, and diabetes. I lost my balance a lot now, I find I am not as quick witted as I used to be. The main one is my memory. I used to have an encyclopedic memory and do still to some extent, but interactions with people, movie plots, I don’t remember as well anymore. But there’s still so much trivia and knowledge that is just stuck in my brain.