Let's say John's age is $x$ years. 
According to the information given, his dad's age is $x+24$ years.
The sum of their ages is 68 years, so we have the equation $x + (x+24) = 68$.
Combining like terms, we get $2x + 24 = 68$.
Subtracting 24 from both sides, we get $2x = 44$.
Dividing both sides by 2, we get $x = 22$.
Therefore, John is $\boxed{22}$ years old.The answer is: 22
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
John is 24 years younger than his dad. The sum of their ages is 68 years. How many years old is John?

### Answer:
