The warning is because too old topics, inactive topics likely are no longer good for discussions but it is not same for all cases. The message is clear, you have to decide that what you want to write is really needed for an inactive topic. If you see it is good, you can write and post it, nothing against you.
I would advise you to lock this thread. You have had enough explanation to what you asked. It is just a notice to you incase you may want to reopen a fresh thread. Posting on old and inactive thread means you want to reawaken the thread, it will be appreciated if your post will be instructive to the thread otherwise you can create a new thread.
Note: Your question have been answered. Please you may decide to lock the thread.