The sum of Zipporah's age and Dina's age is 51. The sum of Julio's age and Dina's age is 54. Zipporah is 7 years old. How old is Julio?
Since Zipporah is 7 years old and the sum of Zipporah's age and Dina's age is 51, then Dina is $51-7=44$ years old.

Since Dina is 44 years old and the sum of Julio's age and Dina's age is 54, then Julio is $54-44=10$ years old.

ANSWER: 10