I’ve noticed that, in general, older people seem to take much longer to learn how to perform new tasks than young people. Has what I have observed been scientifically documented?
If so, what is the explanation for this phenomenon?
Thanks.
As an (almost) old person, I would like to offer a viewpoint you may not have considered.
There is a lot of emphasis placed on something’s being “new,” which is almost universally accepted as being “better.” Older people have seen a lot of “new” things come and go. Eight-tracks were once “new,” as were “quadrophonic” stereos. before webcams, there were attempts to market videotelephones. They were to be the next, best thing… They sucked. After a while, one develops the capability to discern true value from marketing hype and blind mass consumption, and develops a bit of inertia toward taking one’s limited time and energy to learn something which, more than likely, will prove to be no better than whatever it is intended to replace.
Is it a new task or a replacement task?
In my experience, old people (and I’m pretty close to, if not alreay there) learn totally new things at about the same speed as anyone else. However, if it’s a newer way of doing something they already had been doing (e.g., using Windows and a mouse instead of DOS and a keyboard) they’re battling the intertia of changing an already-known pattern.
A second qualifier would be something that requires better than average physical skills. I, to name one person, have neither the visual nor aural acuity I had 10 years ago, so anything that requires close-up work or listening for the little “click” is much harder than it used to be.
In an earlier thread someone asked why old people had trouble using ATM’s and something else that slips my mind (sign of being old). I’ve only used an ATM once, which was to get money for my younger brother and I was driving. It seemed to be easy, but I don’t care to use one. I learned to spend money before ATMs and see them as a means of spending more money at times I don’t need to be spending money. Same goes for many new items. I don’t mind other people using them, but I can do without, thank you.
Your mind can go with age, but from what I’ve observed it has a lot to do with “use it or lose it!”. Some old people stop using their brains and some never did use them. Since I’ve observed that some younger people don’t use theirs (watch Jaywalkers, sometime), there is a message here: Use your brain now or you may become one of those old farts that can’t learn anything new. 
I am not sure, but I think the responses may be missing the point of the OP. I am getting old. I took ancient Greek in college, and I am trying to learn it again and really read some texts that I could not read then. It is more difficult for me to memorize a list of vocabulary words than it was when I was in college. It is more difficult to wrap my brain around a different grammatical form. I can still do it. It takes longer. I would guess it would take me longer to learn to play a musical instrument now than when I was young. I am guessing the OP is asking why? At any rate, I am.