I appreciate the desire to "keep the issue tracker clean", but I think human intelligence needs to be applied to the task, not just a date-based cutoff.
I concur. The older bug reports are ones that have survived past human-based clean-up efforts. They were left open as a reminder, as a todo, to await time or decision by a module author, or it wasn't clear how to solve valid report.
IIRC, there are some for regexes that would take the time of the one or two people supporting that module and the request would cover a not urgently needed corner cases (like handling empty matches or speeding-up badly designed regexes). Those bug reports and rfes are valid and should be left open unless a module author decides that re's won't support the request.