It's very very easy to show that stalegtites are a particular age. Nowadays we can measure their growth over a 10 or 20 year period, and extrapolate how long it took them to grow their full length. The answer will never be 100% precise, but you can achieve a +/- 10,000 years margin of error.
U.S. asks Uzbekistan to join anti-ISIS coalition (Reuters)
from the article: Nature guides may be hiding facts to avoid offending religious hikers