struct not fuc old!!

#include<stdio.h>
struct date{
    int day, month,year;
};
struct date old ={ 32,13,3000};
struct student{
    char name[20];
    struct date bday;
};struct student std[3];
int main(){
    int i=0;
    int oldnum;
    while (i<3){
        printf("enter your name :");
        scanf("%s",std[i].name);
        printf("enter your bday(ex: 00/00/0000) :");
        scanf("%d",&std[i].bday.day); scanf("%d",&std[i].bday.month); scanf("%d",&std[i].bday.year);

        printf("%s %d %d %d\n",std[i].name,std[i].bday.day,std[i].bday.month,std[i].bday.year);
    i++;
    }

    i=0;

    while (i<=3){
        if(old.year<std[i].bday.year){
            old.year=std[i].bday.year;
            oldnum=i;
        }
        else if(old.year<std[i].bday.year && old.month<std[i].bday.month){
            old.month=std[i].bday.month;
            oldnum=i;
        }
        else if(old.year<std[i].bday.year && old.month<std[i].bday.month&&old.day<std[i].bday.day){

            old.day=std[i].bday.day;
            oldnum=i;

        }
        i++;
    }
    printf("%s %d %d %d",std[oldnum].name,std[oldnum].bday.day,std[oldnum].bday.month,std[oldnum].bday.year);



    return 0;
}