If you want people to be an array of pointers, you have to declare it like this:
struct person *people[12];
Remember that declaration follows use and that dereferencing has lower precedence than array indexing; this means that *people[i] is of type struct person, and thus, people[i] is a pointer to struct person.
To initialize each position in people, you call malloc() to make your pointers point to a valid memory location large enough to hold a struct person. It is as easy as:
people[i] = malloc(sizeof(struct person));
When you don't need people anymore, you have to remember to free every memory position you allocated, by calling free(people[i]) for every position i.
I noticed you declared the array to hold 12 structs. This can be dangerous when someone changes the code: it will not work when HOW_MANY is greater than 12. You should declare an array of the same size:
struct person *people[HOW_MANY];
This ensures that your array always has exactly the space needed.
UPDATE:
You need to declare insert as receiving an array of pointers instead of an array of structures:
static void insert (struct person *people[], char *name, int age) {
... }
And people[i].name is invalid. Since people[i] is a pointer now, you need to do it like this:
people[i]->name
Or, equivalently, (*people[i]).name.
The same applies to people[i]->age. Remember to change this both in main() and inside insert.
Also, consider passing i to insert instead of using static variables, unless you have a very good reason to do so. Static variables are used for functions with internal state, and for me, insert is not quite the type of function where you'd want that.
