People don't generally notice a kidney stone until it gets big and causes severe pain. So it's hard to trace back to when it actually started forming.

Well, one scientist decided to age his own kidney stone using carbon dating techniques usually used for dating ancient rock art.  

Guest

• Dr Vladimir Levchenko, research scientist at Australian Nuclear Science and Technology Organisation (ANSTO)
• Dr Gregory Jack Urology surgeon and kidney stone expert 

References

• Nuclear techniques reveal 'stone age': dating kidney stones
• When did your kidney stone start growing? ANSTO scientist carbon dated his to find out | ABC News