About 18 months, laying about 9. My hen has been sitting on a few eggs in the shed for a few days, nothing unusual for her. Today she was on her side. She had an egg buldging from her vent. Her back end was pretty dirty so I washed her off and examined the egg/vent. The tissue at the opening of the vent was black and hardened to the egg (like a scab almost). I used water to soften it. The egg was easily removed with a little help. I didn't try to save it. It fell to the ground. Two more eggs promptly rolled out. Both fell to the ground. All fully formed, hard shelled not larger than average. I put her in a box with some food and water. She seemed relieved immediately. She got up, settled into a new spot...and was dead within 30 minutes.