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Today's date and month is January 1.
Amy's birthday is yesterday, December 31.
The day before yesterday was December 30, previous year.
On December 30 of the previous year Amy was 10 years old.
On December 31 of the previous year Amy got 11 years.
On December 31 THIS year Amy will get 12 years.
On December 31 NEXT year Amy will get 13 years.
Solved.