Which Alice?

ALICE IN PUZZLE-LAND
"Well," said the Mock Turtle, "a man was once sent to prison. To
make his punishment even worse, he was not told how long he
would have to remain in prison."
"That was most unfair!" exclaimed Alice indignantly.
"It sure was!" said the Gryphon.
"Anyway," continued the Mock Turtle, "his gaoler was a very
decent sort of chap, and took a liking to the prisoner.
"'Come on now,' pleaded the prisoner to the gaoler, 'can't you
give me a little hint how long I'll have to stay in this place?'
"'How old are you?' asked the gaoler.
"'I'm twenty-five,' replied the prisoner.
"'And I'm fifty-four,' said the gaoler. 'Tell me, on what day were
you born?'
"'Today is my birthday,' replied the prisoner.
"'Remarkable!' said the gaoler. 'It's also mine! Well, if it's any
help to you, I'll tell you—not that I should, you know, but I will—I'll
tell you that on the day I'm exactly twice as old as you—on that day,
you'll get out.'
"How long does the prisoner have to serve?"
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