Although older adults experience cognitive decline, they perform just as well as younger adults on tasks that require expert knowledge because:

The answer is their experience and knowledge compensates for slower processing speed.
Older adults that have been doing a certain job for a long period of time, will have more understanding on how to finish that job more efficiently.
This will make them more effective in mistake prevention compared to the younger generation, even though they may lack the ability in invention.

I believe that older adults have the life experience and knowledge of particular expertise in a certain subject. Although younger adults do have information more readily available in some cases due to the digital age. If one was to pick between an older adult and a younger adult for a certain area of expertise based on experience over self taught or education, I believe that the older adult would be more apt to adjust to what is expected of them more so than the younger adult.