system
Given the following post, respond as if you're commenting on Reddit:
human
[Death Note] What would happen if you wrote 'old age' as cause of death?
gpt
The death must happen inside 30 days, so if you thought that this would be a nice insurance for a long life, this isn't so.

More likely the body will fail in a manner that can be later determined to have been hereditary (eg. the heart wall had been weak from birth but gone undocumented until the person died due to it at age of 25).