My tkcalendar Entry is setting 2000 for years before 2000, example if you answer your bithdate is 1986 it consider you being born in 2086.

birthDateEntry = DateEntry(root, width=12,background='darkblue', foreground='white', borderwidth=2,font = ("Copperplate Gothic Light", 10))

student = Student(fullNameEntrada.get(), birthDateEntry.get_date().strftime("%m/%d/%Y").replace("-", "/"))
        #For a 5/13/1989 it returns
        print(birthDateEntry.get()) #Return 5/13/2089
        print(birthDateEntry.get_date()) #Return 2089-05-13

#student class
class Student():
    
    def __init__(self, name, birthdate):
        self.name = name
        self.birthdate = birthdate
        self.age = self.getAge()
        self.registerDate=str(date.today().strftime("%m/%d/%Y").replace("-", "/"))      
        self.connection = sqlite3.connect('students.db')
        self.cursor = self.connection.cursor()
        self.createTable()


#getAge Method on student class
def getAge(self):
        today = date.today()
        birthyear = self.birthdate.split()
        self.age = today.year - int(birthyear[0][6:])
        return self.age```