I have noticed that some new sandbox posts are being shutdown as duplicates of other much older posts. There is nothing wrong with that.
But I think there should be a time limit after which challenges can be reused.
Specifically because of new langauges that allow for shorter solutions, and because they can still be fun!
I understand that the we don't want copying answers and such, but that doesn't mean that the challenge can't be done again.
I also know that we allow non-competing answers with newer languages.