To solve this problem, we need to set up equations based on the information given:

1. Let's denote the current age of the son as \(S\) years.
2. According to the problem, the father is 3 times as old as the son. Therefore, the father's current age is \(3S\) years.
3. The problem further states that in 13 years, the father will be twice as old as the son. This translates into the equation: 
   \(3S + 13 = 2(S + 13)\)
4. Let's solve this equation for \(S\):

Thus, the present age of the son is 13 years.

Verification:

Let's verify the solution with the given condition:

• Current age of the son: \(13\) years. Therefore, the father's current age is \(3 \times 13 = 39\) years.
• In 13 years, the son's age will be \(13 + 13 = 26\) years, and the father's age will be \(39 + 13 = 52\) years.
• The father will indeed be twice as old as the son: \(52 = 2 \times 26\).

This confirms that our solution is correct. Therefore, the correct answer is 13 years.