In my opinion an educative/quality post can't be outdated.
If a plagiarist is or an unworthy post is found after 10 years, wouldn't he/she be banned or the post get deleted ?
It shouldn't matter how long a post has been so far it is considered helpful or merit-worthy, and moreover as a user I guess I've barely read about 0.1% of the thread on here and should I come across a post that I learn something new from or find helpful I shouldn't give it merit simply because of when it was posted ?