Yes, this is the alternative way I meant. No manually selection of outdated threads, only one klick and all outdated (older than ...) threads are locked. Simply "half", ... no, better "semi automatted locking".

But maybe one or some old threads should stay open. Therefore you need further the manually selection.

You can already get that functionality. The individual thread lets you lock/unlock it & if you go to Manage Posting, you can lock all threads where the last response is more than X days old.