Since pre- means before, and post- means after, using both in the same word would be...

I am best when I am long, standing tall and straight, I look my best when stiff and firm, a truly proud estate, I’m known to release some sticky sap when fully grown and ripe, And if you handle me too much, you’ll need a cloth to wipe.

I know it's late summer now, but before you know it, this season will show up out of nowhere!

I spend my whole life helping people get somewhere I’ll never be.

My daughter’s favorite riddle is this: What looks like a celestial body without being said celestial body?