OOP JS (calculate age)

JavaScript

function Student(fullName, birthday, major, email, studentId, city, state, age)
{
    this.fullName = fullName;
    this.birthday = birthday;
    this.major = major;
    this.studentId = studentId;
    this.city = city;
    this.state = state;
    this.age = age;

    this.getAddress = function()
    {
        return this.city + " " + this.state;
    }
}

Student.prototype.age = function() {
    var toDate = new Date();
    var fromDate = new Date(this.birthday), age = [];
    ydiff = y[0] - y[1],
    m = [toDate.getMonth(), fromDate.getMonth()],
    mdiff = m[0] - m[1],
    d = [toDate.getDate(), fromDate.getDate()],
    ddiff = d[0] - d[1];

    if(mdiff < 0 || (mdiff === 0 && ddiff < 0))
    {
        --ydiff;
    }

    if(mdiff < 0)
    {
        mdiff += 12;
    }

    if(ddiff < 0)
    {
        fromDate.setMonth(m[1] + 1, 0);
        ddiff = fromDate.getDate() - d[1] + d[0];
        --mdiff;
    }
    if(ydiff> 0) 
    {
        age.push(ydiff+ ' year'+(ydiff> 1? 's ':' '));
    }
    if(mdiff> 0) 
    {
        age.push(mdiff+ ' month'+(mdiff> 1? 's':''));
    }
    if(ddiff> 0) 
    {
        age.push(ddiff+ ' day'+(ddiff> 1? 's':''));
    }
    if(age.length>1)
    {
         age.splice(age.length-1,0,' and ');    
    }
    return age.join('');
}

var Students = [];

 var student = new Student("Ly Manh Long", 1996/07/20, "Engineering", "[email protected]", "1431200008", "Thu Dau Mot", "Binh Duong", 1);
 Students.push(student);