qsort() in struct

[VergilDevil123]

 typedef 
    struct zoz
    {
         int age;
         int mag;
         int suly;
    }
    nevsor_t;
    int olvas(nevsor_t * pnevsor)
    {
        return scanf("%d %d %d",
            &pnevsor->age, &pnevsor->mag, &pnevsor->suly);

    }
    int kiir(nevsor_t nevsor)
    {
        return printf("%d year\t%d cm\t%d kg\n",
            nevsor.age, nevsor.mag, nevsor.suly);

    }
    int sort_age(const void *a, const void *b)
    {
        struct nevsor_t *ia = (struct nevsor_t *)a;
        struct nevsor_t *ib = (struct nevsor_t *)b;

         return *ia->age - *ib->age;
    }

I want to sort the elements of block tomb by age which is the first variable of struct nevsor_t.
The elements are added manually from the keyboard:

int main()

{
            int i,n;
            nevsor_t tomb[50];
            nevsor_t t;
            printf("Add meg a resztvevok szamat:");
            scanf("%d", &n);
            printf("\n");
            for (i=1;i<=n;i++) {
                printf("%2d. resztvevo adatai: ", i);
                olvas(&t);
                tomb[i]=t;
            }
            qsort(tomb, n, sizeof (tomb[0]), sort_age);
            for (i=1;i<=n;i++) {
                printf("%d. : ",i);
                kiir(tomb[i]);
            }
        return 0;
        }

And the problem is with this line:
return *ia->age - *ib->age;
"ia" and "ib"---pointer to incomplete class type is not allowed.
Any ideas how could I fix this kind of problem?

[Ancient Dragon]

Corrected function. nevsor_t is NOT a structure, it's a typedef, so you don't use the struct keyword with it. Also, there is no * before ia->age because ia is not a double pointer.

    int sort_age(const void *a, const void *b)
    {
        nevsor_t *ia = (nevsor_t *)a;
        nevsor_t *ib = (nevsor_t *)b;

         return ia->age - ib->age;
    }