How to get elements of JSONObject?

JSONObject json = new JSONObject(yourdata);
String statistics = json.getString("statistics");
JSONObject name1 = json.getJSONObject("John");
String ageJohn = name1.getString("Age");

For getting those items in a dynamic way:

JSONObject json = new JSONObject(yourdata);
String statistics = json.getString("statistics");

for (Iterator key=json.keys();key.hasNext();) {
    JSONObject name = json.get(key.next());
    //now name contains the firstname, and so on... 
}

You did not specify which library you intend to use to represent the JSON object. Usually there are methods to enumerate the properties of the object. For example:

org.json.JSONObject.keys()

returns an iterator of the String names in the object.