Doomsday565

I was re reading isle of emberdark and realized that something didn't make sense from what's been implied about investecher is that if you have enough you won't age(im not 100% sure of this but remember seeing WOB on other form post that made this seem to be the case) which brings up the question how the hell can dragons age as they are by far some of the most highly invested beings in the cosmere probably only less invested then the shards themselves. So how come they aren't ageless and though they live a remarkably long 20,000 year that's far from truly ageless. And it's implied that they die of old age around 20,000 years old. The only thing I can think to explain this is that beings like the returned and any one at the 5th hightning aren't actually ageless and whould die if they managed to live 20,000 years I guess 20,000 years could also be the point when dragons get so old they essentially decide to stop living though I feel like this doesn't make much sense.