$username = $_POST["username"];
$password = $_POST["password"];

$statement = mysqli_prepare($con, "SELECT * FROM user WHERE username = ? AND password = ?");
mysqli_stmt_bind_param($statement, "ss", $username, $password);
mysqli_stmt_execute($statement);

mysqli_stmt_store_result($statement);
mysqli_stmt_bind_result($statement, $id, $name, $username, $email, $age, $password);

$response = array();
$response["success"] = false;

while(mysqli_stmt_fetch($statement)){
    $response["success"] = true;
    $response["name"] = $name;
    $response["username"] = $username;
    $response["email"]= $email;
    $response["age"] = $age;
    $response["password"] = $password;

}

echo json_encode($response);
?>

import android.app.ProgressDialog;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.toolbox.Volley;

import org.json.JSONException;
import org.json.JSONObject;

public class RegisterActivity extends AppCompatActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_register);

    final EditText etAge = (EditText) findViewById(R.id.etAge);
    final EditText etName = (EditText) findViewById(R.id.etName);
    final EditText etUsername = (EditText) findViewById(R.id.etUsername);
    final EditText etPassword = (EditText) findViewById(R.id.etPassword);
    final Button bRegister = (Button) findViewById(R.id.bRegister);
    final EditText etEmail=(EditText) findViewById(R.id.etEmail);

    assert bRegister != null;
    assert bRegister != null;
    bRegister.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            assert etName != null;
            final String name = etName.getText().toString();
            assert etUsername != null;
            final String username = etUsername.getText().toString();
            assert etAge != null;
            final String age = etAge.getText().toString();
            assert etPassword != null;
            final String password = etPassword.getText().toString();
            assert etEmail != null;
            final String email = etEmail.getText().toString();

            Response.Listener<String> responseListener = new Response.Listener<String>() {
                private ProgressDialog loading;
                @Override
                public void onResponse(String response) {
                    try {
                        JSONObject jsonResponse = new JSONObject(response);
                        boolean success = jsonResponse.getBoolean("success");
                        loading = ProgressDialog.show(RegisterActivity.this, "Please wait...", "Registering...", false, false);
                        if (success) {
                            Intent intent = new Intent(RegisterActivity.this, LoginActivity.class);
                            RegisterActivity.this.startActivity(intent);
                        } else {
                            AlertDialog.Builder builder = new AlertDialog.Builder(RegisterActivity.this);
                            builder.setMessage("Register Failed")
                                    .setNegativeButton("Retry", null)
                                    .create()
                                    .show();
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            };

            RegisterRequest registerRequest = new RegisterRequest(name, username, email, age, password, responseListener);
            RequestQueue queue =    Volley.newRequestQueue(RegisterActivity.this);
            queue.add(registerRequest);
        }
    });
}