What is the ruling on jesting with women online, and is it permissible for a man to communicate with them for long periods under the pretext of discussing educational matters? Furthermore, what is the validity of citing the Prophet's (PBUH) saying, "No old woman will enter Paradise," as evidence for this?

The relationship with this man should be severed immediately, and the explanations he provides should be replaced with books and educational websites. One must be wary of a woman being the cause of misguidance and deviation for a preacher and a حافظ لكتاب الله (one who has memorized the Book of Allah) who has begun to tread a deviant path.