For as long as I've been writing, I've been skeptical of people saying, "I'm aiming for thus and thus amount of pages." Not only does that seem entirely out of your control, but it's also an entirely flexible quantity due to formatting technology.
It's out of your control. A story is going to take up as much space as it needs to. It is true that editing is a superpower that'll give you some control over length after the writing has been done. But when you're writing, how can you say you're aiming for a particular page count? You'll either be cramming and leave out necessary bits, to make the story shorter. Or you'll be bloating, and the story will drag. Or you're a lucky bastard, and your guesstimation is spot on. That last one isn't likely, you bastard.
Thinking on editing: I will argue that editing gives you some power over the length of a story. Rephrasing things, rearranging things, compositing things, general mishing and mashing, the editing process, in short: anything can be mangled, braided, woven, and welded into just about any shape. When you come to the end of things, though, I cannot believe that a story doesn't dictate its own necessities. What IS in it when finished it becomes--in an honest and sober judgment of finishedness--is all of and only what needs must be in it. Like poetry: every word justifies its place and placement. Like one of them puzzly, with the sticks things, that's like a tower, and the displacement of one piece sends the whole thing cascading to a torrential mess of shapelessness.
That's how it OUGHT to work. Civilized writing ought to have all of, and only, what it most perfectly requires. Inside the boundaries of "well, it's cool, so shut up", obviously.
Having said all that, I'm wondering about those times when your guesstimation is so astronomically off you can't even figure it out. At the moment, I'm writing what I really hope shapes into a short story. I've gotten to page seventeen, and my reckoning puts my plot at less than half done. My hope was eighteen pages, my range went to thirty. Basically, the math is off. I don't know why, but the scenes are taking up more pages than they feel like before I write them down. I don't know if that means I'm putting in way too much, or my estimation is just really off. I've decided to not really worry about it. It can take the shape it ought to take. That's the idea.