The correct option is A 18 years
Let the father was x years of age when his son was born. Now, when his son is 'x ' years old, obviously, father is '2x' years old.
Given, age of Father = 46 years
Therefore, son's present age = 23 years
So, the son was 18 years of age 5 years back.
Hence, option (A) is the correct answer.