Trying to calculate a person's age using pointers

age.c

#include <stdio.h>

int age(int* year);

int main()
{
    printf("Enter your birth year: ");
    char buf[50];
    char* input = gets(buf);
    int year = atoi(input);
    int* year_ptr = &year;
    int output = age(year_ptr);
    printf("You're %d years old.\n", output);
    return 0;

}

int age(int* year)
{
    return 2012 - *year;
}