To solve this problem, let's first set up an equation based on the given information.
Let's assume John's current age is represented by "x".
Five years ago, John's age was "x - 5".
In 8 years, John's age will be "x + 8".
According to the given information, John's age five years ago was half of the age he will be in 8 years. Mathematically, we can write this as:
x - 5 = (1/2)(x + 8)
To solve this equation, we can multiply both sides by 2 to eliminate the fraction:
2(x - 5) = x + 8
Expanding the equation:
2x - 10 = x + 8
Now, let's solve for x:
2x - x = 8 + 10
x = 18
Therefore, John is currently 18 years old.
The correct answer is option D.