"I will guess your age" game not working properly

I tried to make a really simple "I will guess your age" game. When I say that I haven't had birthday this year, it works just fine, but when I say that I had birthday this year, it does the same thing as when I say I didn't. For example, when i say that i was born in 2000 and say that i haven't had birthday this year, it would say that I'm 19 years old, which is correct. But when I say that I had birhday this year, it also says that I'm 19, which is, obviosly, not correct. Can someone please tell me where is the problem? Any help would be appreciated, thanks.

import java.util.Scanner;

public class kouzlo {
    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        int currentyear = 2020;
        System.out.println ("Welcome! I can guess your age. What year were you born?");
        int yearofbirth = scanner.nextInt();
        System.out.println ("Have you had your birthday this year?");
        boolean yes, Yes, YES, y, Y = true;
        boolean no, No, NO, n, N = false;
        boolean hadbirthday = scanner.hasNextBoolean();
        int summary = currentyear - yearofbirth;
        int summary2 = currentyear - yearofbirth - 1;
        if (hadbirthday == true) {
            System.out.println("You're " + summary + " years old!");
        }
        else {
            System.out.println("You're " + summary2 + " years old!");
        }
    }
}

To answer your question, the comment of Federico is right. You need to do something like:

boolean hadbirthday = false;

if (scanner.hasNextBoolean()) {
  boolean hadbirthday = scanner.nextBoolean();
};

I also see these lines:

boolean yes, Yes, YES, y, Y = true;

boolean no, No, NO, n, N = false;

which seems to be useless. If you want to allow the user to enter one of those and interpret it as a boolean, you will have to use hasNext() / next() and check if the resulting string matches one of your patterns.