People suggest that age might result in slower fingers, but I actually find that hard to believe. I'm a keyboardist (piano/organ/electronic keyboards), and I'm known for being very fast-fingered. I don't think I'm any slower playing now than I was when I was 20 - if anything, I'm faster. But maybe it's the ability to learn new fast moves with fingers that goes down as you get older? So I'll always be fast playing keyboard instruments because I learned to be fast when I was young, but I can't duplicate it on cubing because I learned the moves too late? (If only I had known about fingertricks - and had something other than a Rubik's - when I first learned to solve a cube at age 18!) Since Ron van Bruchem learned to be fast at a somewhat younger age, perhaps that's why he's so much faster than me? And perhaps that means he'll always be fast, because he learned early enough?
I still suspect I could get fast if I REALLY worked at it. But I admit I find it more fun to really work at BLD instead - I get results more quickly with BLD when I work on it than I do with speed.