PROBLEM:
If you add the age of a man to the age of his wife, the result is 91.  He is now twice as old as she was when he was as old as she is now.

How old is the man and his wife?
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SOLUTION:
The man is 52 and his wife is 39.

The puzzle refers to the man as once being as old as the wife is "now."  This gives you the first important piece of information; the man is older than the wife.  Second, you know that the two ages will add up to 91.  Third, you know that their difference in age is a constant variable.  You can't, however, assume that they are close in age, but they must both be middle aged, otherwise it would be difficult to generate a number as high as 91 under the parameters of the problem.

So, after gathering this information, and some guess and check work, you'd find that the man is now twice the age (52) of her age (26) when he was the age she is now (39).