Xiao Lin's age is the same as her sister's, that is, the age difference between Xiao Lin and her sister-Xiao Lin's age.

Xiao Lin is my elder sister's present age, and her elder sister is 3 1 year old, that is, the age difference between Xiao Lin and her elder sister is 31-her elder sister's age.

So the age difference between Xiao Lin and his sister is (31-1)/3 =10 years old.

So Kobayashi's age now is 31-10-10 =11year.