1200 years. Of course this dragon would live past its average lifespan. Why wouldn't it? It's not like you had anything better to do than squeezing out dragon turds... You were convinced that the universe just kept going out of its way to make your pitiful existence even worse. Unfortunately, you didn't yet understand the extent of this hell you were trapped in.
...
Your elderly dragon host slowly walked along his cave before curling up in his nest. His tail pressed into your face, blocking most of your view, save for a small peek at his scaly feet. It was finally happening. The dragon was about to die and you couldn't me more excited. You'd dreamed of this moment for centuries, and it was finally here. Your mind was racing. What would happen to you? There's no afterlife for dragon body parts, so would you just fade away? The unknowns would have terrified you if you weren't so anxious to be free from your asshole body.
The dragon laid his head down, his breathing slowed, and finally, he released his last breath. Over the next minute, your world began fading to a dull grey. Then suddenly, there was nothing.
...
As you floated through the void, you felt a weird pull. Like you were tethered to another soul. This other soul was being pulled towards some unseen destination, and you were drug along with it. Everything around you was so abstract and alien. Time had no meaning. Suddenly, the soul was fused into an ovoid mass, absorbing your soul along with it. And once again, everything faded to nothingness.
...
Your world stirred as you felt like you were waking up. The world was still dark and your senses were numb. You were in a new body, but the form had some amount of familiarity to it. As you tried to make sense of your surroundings, there was movement around you. A sudden squishing and stretching before something around you cracked and light began to pour in. Before long, the shell around you fell away and you could see the world around you. You were in some sort of cave filled with glowing crystals. From your vantage point, you could see the cave open up to a cliffside with a valley down below. You tried to lift yourself up, but found that you couldn't make yourself move. This was a feeling you'd become all to familiar with in your past life and didn't like this one bit. As you tried to make sense of things, you could see the lower half of two full-grown dragons looking down at you. While frantically trying to figure out what you were, a familiar appendage suddenly lowered down into your view. A black and gold scaled dragon tail.
"But that means... I'm... I'm still a dragon's tailhole?" A deep all-consuming terror rushed through your mind.
"No! This.. This can't be right! No. No! NO! NO NO NO!" You desperately tried to scream for help, but your body was not yours to control. The dragon's magic not only merged you into part of his body, but also bound your soul to his. For the rest of eternity, you would be reborn as the anus of the dragon's reincarnated body. The curse maintaining your full awareness was also intact, meaning that you were eternally, permanently aware of the eons of dragon poop you would be passing. And to think, all this because you unwittingly stumbled into a dragon's lair all those years ago.
As mourned your future, a familiar pressure built up behind you as the hatchling prepared for its first poop. As your lips parted and the turd slicked through, you mentally cried for help. But help would never come, as you had no control and were doomed to spend eternity as a dragon's tailhole.