Anyone have a commit hook for forbidding old branches from being merged in?

I work on a web application that due to underlying database schema
changes etc only even compiles and runs for a given 2 week moving
window.

Thus if someone started a branch say 1 month ago, works on it one and
off, and then merges it back into the mainline it becomes impossible
to bisect that code if it has a problem. You either have to:

 * Revert the whole merge
 * Manually eyeball the code to see where the error might be
 * Brute-force manually bisect it by checking out only the files
   altered in those commits instead of the commit at a given
   data. Usually individual files are still compatible with the new
   code.

But the whole reason this is a problem is because people don't rebase
their branches before merging them in, unintentionally causing
problems.

So before I write a hook to do this, is there anything that implements
a hook that:

 * Checks if you're pushing a merge commit
 * If so, is that merge based off and old version of $MAINBRANCH
 * Is the base of that branch more than N days old?
 * If so reject the push