Rank the stars based on their current age, from oldest to youngest. if two (or more) stars have approximately the same age (that is, ages within a few million years), rank them as equal by dragging one on top of the other(s).

How fine do you want them categorized for the ranking ?
What's the population to be ranked ?
The 4000 naked-eye-visible stars ?
The stars within, say, 50 light years from Earth ?
All 200-400 billion stars in the Milky Way galaxy ? 
All the stars in some other galaxy ?

Or did you have a list of items to be ranked that you decided not to share ?
That would be a lot like asking us to seat a class of sixth graders alphabetically,
and then not telling us their names.

And how do we drag one star on top of another ?
And if I do that here, how will you know about it ?

The answer should be a.