Learn Turkish: Yönetmen yaşlı adamı sandalyeye oturtuyor. - The director is making the old man sit on the chair.

This ties into the core rule of causative verbs! The original verb oturmak (to sit) is intransitive, meaning it doesn't take a direct object. When you make an intransitive verb causative, the person being made to do the action (the causee) becomes the new direct object and must take the accusative case (adamı).

Does the dative case on sandalyeye have anything to do with the causative rule?

No, it doesn't. The word sandalyeye takes the dative case simply because it is the destination of the sitting action (literally 'sitting to' the chair). The causative rule only cares whether the original verb takes a direct object, regardless of what other case-marked nouns are in the sentence.

Wait, doesn't English say 'sit on the chair'? Why use the dative case (sandalyeye) instead of the locative (sandalyede)?

In English, we focus on the final position (on the chair), but Turkish treats the act of taking a seat as a movement towards a destination. Therefore, verbs like oturmak or oturtmak require the dative case (-e/-a) for the object being sat upon. If you used sandalyede, it would sound like the old man was already sitting on the chair while the director made him perform the action.

Why is the causative suffix -t here (oturtuyor) instead of the more common -tır?