How can I calculate the age of a person in year, month, days?

Question

I want to calculate the age of a person given the date of birth and the current date in years, months and days relative to the current date.

For example:

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Answer 1

The Swift implementation of dreeves' answer.

ps. instead of (y,m,d) (ynow,mnow,dnow) as the inputs, I use two NSDate's, which may be more handy in real world usages.

extension NSDate {

    convenience init(ageDateString:String) {
        let dateStringFormatter = NSDateFormatter()
        dateStringFormatter.dateFormat = "yyyy-MM-dd"
        dateStringFormatter.locale = NSLocale(localeIdentifier: "en_US_POSIX")
        let d = dateStringFormatter.dateFromString(ageDateString)!
        self.init(timeInterval:0, sinceDate:d)
    }

    func ageFrom(date: NSDate) -> (Int, Int, Int) {
        let cal = NSCalendar.currentCalendar()

        let y = cal.component(NSCalendarUnit.Year, fromDate: date)
        let m = cal.component(NSCalendarUnit.Month, fromDate: date)
        let d = cal.component(NSCalendarUnit.Day, fromDate: date)
        let ynow = cal.component(NSCalendarUnit.Year, fromDate: self)
        let mnow = cal.component(NSCalendarUnit.Month, fromDate: self)
        let dnow = cal.component(NSCalendarUnit.Day, fromDate: self)

        let t0 = y * 12 + m - 1       // total months for birthdate.
        var t = ynow * 12 + mnow - 1;   // total months for Now.
        var dm = t - t0;              // delta months.
        if(dnow >= d) {
            return (Int(floor(Double(dm)/12)), dm % 12, dnow - d)
        }
        dm--
        t--
        return (Int(floor(Double(dm)/12)), dm % 12, Int((self.timeIntervalSince1970 - NSDate(ageDateString: "\(Int(floor(Double(t)/12)))-\(t%12 + 1)-\(d)").timeIntervalSince1970)/60/60/24))
    }

}

// sample usage
let birthday = NSDate(ageDateString: "2012-7-8")
print(NSDate().ageFrom(birthday))