def years_before(year = 0)
      Age.new(birthday: birthday, present_day: present_day.prev_year(year))
    end
def years_before(year = 0)
      Age.new(birthday: birthday, present_day: present_day.prev_year(year))
    end
Get Happybirthday::Age object which has past date
 @param year [Integer] number of years
 @return [Happybirthday::Age]