To an economist or a journalist who is used to thinking of a decade as long enough for entire theories to rise and fall, an age is the longest period imaginable; durable ideas can be age-old and this age is synonymous with 'this world' or 'everything'.
Can anyone explain why thinking, and not think is used in that passage?
Would it be ungrammatical replacing thinking with think?
Or, otherwise, that replacing would be grammatical but it would produce a change in meaning. If so, can anyone explain what this change in meaning is?