I've had clumsy moments as time goes on, and I've thought about this before, but in my case I can chalk it up to two big things:
1.) I've gained weight, and I believe there's a correlation between aging and gaining weight. Certain maneuvers are noticeably harder. I seem more top-heavy than in my memories of being younger.
2.) I have KIDS. I have almost died so many times because we're disorganized and my kids' crap is EVERYWHERE. I've had one broken toe, countless foot bruises, surprise falcon kicks to baby skulls, and several instances of "Why, child, have you crawled under my feet, from behind me, while I briskly walk to the bathroom? Well I don't want to maim or kill you, so....Guess I'll die aka avoid putting any weight on that foot and toss my body as far away from theirs as possible during planetfall btw Did you know plastic cups explode if crushed just right?" Likelihood of having kids correlates with age, I assume.
Now...you listed several mental things besides physical. So I guess I'm only speaking to physical clumsiness :P