add method get age in ms for Message class

[apirom9]

add method get age in ms for Message class

[Tembrel]

Does this really carry its weight? If so, how about:

  public long getAge(TimeUnit unit) {
      Date date = getDate();
      if (date == null) {
          return Long.MIN_VALUE; // Long.MAX_VALUE?
      } else {
          long ageMillis = System.currentTimeMillis() - date.getTime();
          return unit.convert(ageMillis, TimeUnit.MILLISECONDS);
      }
  }

You want to be able to distinguish the case of the age being 0 from the case where there is no date.