fitness membership calc

#include <iostream>
#include <string>
#include <limits>
#include <cmath>
#include <iomanip>

void displayMenu();
void getInput(int& age, int& months, int& ptChoice);
void calculateMembership(int& age, int& months, int& ptChoice, double& membership, double& PTtotal);
using namespace std;

int main()
{
    // Write your main here

    int age = 0;
    int ptChoice = 0;
    int months = 0;
    double PTtotal = 10.00;
    double membership = 20.00;

    displayMenu();
    getInput(age, months, ptChoice);
    calculateMembership(age, months, ptChoice, membership, PTtotal);

    return 0;
}

void displayMenu()
{
    cout << "\n                           ****Fitness Menu****                           " << endl;
    cout << "          ********************************************************          " << endl;
    cout << "                  Basic Membership Price:$20.00 per month.                  " << endl;
    cout << "                  Senior Discount:                     30% off              " << endl;
    cout << "                  12 month special:                    15% off              " << endl;
    cout << "                  Sign up for more than 5 PT sessions  20% off              " << endl;
};

void getInput(int& age, int& months, int& ptChoice)
{
    cout << "\nPlease answer the following information to calculate your monthly membership costs.";
    cout << endl
         << "Please enter your age: ";
    cin >> age;
    cout << "How many months do you wish to purchase a membership? ";
    cin >> months;
    cout << "How many personal training sessions have you paid for?: ";
    cin >> ptChoice;
};

void calculateMembership(int& age, int& months, int& ptChoice, double& membership, double& PTtotal)
{
    double overallTotal;
    double overallPTtotal;
    double grandTotal;

    if (age < 18) {
        cout << "***You must be at least 18yrs of age or older.***";
    }

    if (age >= 65 && months >= 12) {
        membership = membership - (membership * .45);
    }
    if (age >= 65 && months < 12) {
        membership = membership - (membership * .30);
    }
    if (age < 65 && age >= 18 && months >= 12) {
        membership = membership - (membership * .15);
    }
    if (age < 65 && age >= 18 && months < 12) {
        membership = 20.00;
    }

    if (ptChoice > 5) {
        PTtotal = PTtotal - (PTtotal * .20);
    }
    if (ptChoice < 5) {
        PTtotal = 10.00;
    }

    overallTotal = membership * months;
    overallPTtotal = ptChoice * PTtotal;
    grandTotal = overallTotal + overallPTtotal;

    cout << "\nThis is your monthly Membership rate: $" << setprecision(2) << fixed << membership;
    cout << "\nThis is your total Membership cost: $" << setprecision(2) << fixed << overallTotal;
    cout << endl
         << "\nThis is your Personal Training cost per session: $" << setprecision(2) << fixed << PTtotal;
    cout << "\nThis is your total Personal Training cost: $" << setprecision(2) << fixed << overallPTtotal;
    cout << endl
         << "\nThis is your Grand Total: $" << setprecision(2) << fixed << grandTotal;
};