The article links to a paper which estimates how much more effective you get at reading the more knowledge you have. It shows that for most ages you don't improve in this way, but for older ages you do.
Then it says for the "best case" that "adults" takes years to get twice as effective at reading.
If you don't believe this then it means you think it takes adults less than a year to get twice as effective? If effectiveness doubles each year then that would mean by the time a 25 year old becomes 65 that they're 1 million times as effective at reading than when they were 25. Does that sound reasonable to you?
Then it says for the "best case" that "adults" takes years to get twice as effective at reading.
If you don't believe this then it means you think it takes adults less than a year to get twice as effective? If effectiveness doubles each year then that would mean by the time a 25 year old becomes 65 that they're 1 million times as effective at reading than when they were 25. Does that sound reasonable to you?