On a task with no due date there's nothing for the reminder process to indicate that you would need reminding about it. My best suggestion is to create a smart list with the following search;

due:never

This will list all tasks without due dates into a single list. You can then review that regularly (part of your weekly review if you're a GTDer). Alternatively, start prioritising these tasks and assigning due dates.

Not good enough. If you are a GTDer, a significant percentage of your tasks won't have due dates. It is difficult to flag the 'old' ones in the weekly review.

There needs to be a way to identify 'old' tasks within a particular search or list. Sort by "creation date" would be fine.

How about adding the addedBefore: parameter then. For example:

addedBefore:"1 month of today"

will only list tasks created more than a month ago. This can be modified for the required period you deem to be "old".

You can set a daily repeating task to review old tasks, and have that arrive by IM and/or email every day.

Yes, in the GTD methodology, you are strongly discouraged from putting due dates on tasks that really have no due date, which is MOST of them. That said, I really need a way to put a "not to exceed" time limit on some things, which this would do.

It would be nice to be able to receive notifications for tasks that have start dates, even if they have no due dates.

+1