When were the carlsbad caverns created?

Answer 1

Caves don't just appear as single, complete entities as you imply. They take many tens or hundreds of thousands, possibly a few million, years to form; and different series of passages and chambers within the system form at different times and take different times to form.

The oldest parts of Carlsbad Caverns date back at least 4 million years, with their "inception" stretchign back before that; and if any of its passages still carry streams, those passages are said to be "active" and are still being formed.

Caves don't really stop developing as the abandoned or "fossil" passages of a cave are in a state of slow decay by percolating ground-water attacking the limestone above the passages. This does NOT as sometimes thought, form chambers etc, but brings about occasional collapses when not forming stalactites and stalagmites.