You are close. If you store the the gender of each person in an array, you can do it like this:

String[] persons = new String[100]
for (int i = 0; i < persons.length; i++) {
  if (i<60) {
    persons[i] = "female";
  }
  else {
    persons[i] = "male";   
  }
}

Alternately, if a person is more than a gender, consider making a class Person that holds a gender field, and then have an array of Persons. You would set the gender in a similar way.

You might use a Map<String,String> where the key is your "variable name" and the value is the value of that variable.

You will need a String[] of some size that you can determine dynamically.
Then, assign values to the array elements.

String[] anArray;

// some magic logic

anArray = new String[100];
for(int i = 0; i < anArray.length; i++){
 // more magic logic to initialize the elements
}  

Another option is a Vector<> or ArrayList<> like so:

List<String> anExpandableArray = new ArrayList<String>();
// add String data
anExpandaleArray.add("Foo");
anExpandaleArray.add("Bar");

When you find yourself wanting to create "more variables" of the same type, you usually want a list of some kind. There are two fundamental kinds of "lists" in Java: Arrays, and Lists.

An array:

String[] people = new String[10];               // That gives you room for 10

people[0] = "female";
people[1] = "male";
// ...
int n = 1;
System.out.println("Person " + n + " is " + people[n]);

A List:

List<String> people = new LinkedList<String>(); // Expandable
people.add("female");
people.add("male");
// ...
int n = 1;
System.out.println("Person " + n + " is " + people.get(n));
// Note difference -------------------------------^^^^^^^

Using an array is great when you know in advance how many there will be. Using a list is great when you don't know how many there will be.

Note on lists: There's an interface, List, and then there are multiple different concrete implementations of it with different runtime performance characteristics (LinkedList, ArrayList, and so on). These are in java.util.

Just Use an array like so

String[] people = new String[numofelements];

And to initialise the array

for(int i = 0; i < people.length; i++){
      people[i] = "whatever";
}

String[] persons = new String[101];

for (int i = 0; i < 101; i++) {
    if (i < 60) {
       String persons[i] = "female";
    } else {
       String persons[i] = "male";   
    }
}