For requiring me to take a course on Victorian-era English literature as part of my engineering degree graduation requirements? By forcing me to take the course, they literally filled my brain up with useless stuff which will accelerate the onset of age-related dementia.
No, that's not useless. If you were paying attention it may have forced you to learn some proper English. I'm not sure if the summary headline fits the article content completely. TFA seems to be trying to say (caveat. I'm not a psychologist and I only read TFA and parts of the paper) is something to the effect that for example: in the old days when there was no internet or the net was more limited than it is now, you had to solve your own problems and that stimulates your brain and 'trains' it. A person who has the internet at his/her disposal and solves most of their problems by hitting experts-exchange, stack overflow or some such web and benefits from hard thinking done by others does not have their brain stimulated in the same way because they don't have to remember this stuff and don't figure it out on their own. They can just book mark it whereas 20 years ago you 'd better write yourself a private howto once you solved your conundrum in case you ran into this again five years and that makes things concerning the problem it self stick a bit more than hitting [Ctrl]+[D]. If you just use search engines to search for solutions to problems the information retained probably has more (though not exclusively) to do with how to find the solution than how to figure the problem out by yourself. Basically if you are hit by tough problems when you are younger and forced solve them yourself and to exercise your brain it means that when you get older it takes you longer to remember things because you have to 'search a bigger database'. not because your brain is getting slower. Furthermore if your short term memory and analytic abilities decline with age you can make up for it with experience, expertise and 'brain training' received in your youth. Finally, as you age, you also gain the ability to notice subtle side effects of doing something as you get older that a younger person does not notice as a result of your brain being trained more and having more experience. Something like:
Younger person: If we connect this doohickey with that thingemabomb we get effect X.
Older person: Hmmmmm.....
Younger person: (impatiently annoyed) What!
Older person: Well, that's true but if somebody then presses button A while dohickey is in state Y the thingemabob will short out.
Younger person: (slightly embarrased) Oh, yeah right.