Was Prophet Abraham commanded to debate his people and invite them to worship Allah, or did he debate them by his natural inclination and the exertion of his intellect, and when did revelation descend upon him?

There is no explicit text stating when Ibrahim (peace be upon him) was granted prophethood. What is mentioned about his age when he contemplated the stars comes from reports of the Children of Israel, which are not reliable. The Holy Quran affirms that Allah granted him wisdom and his decisive argument from a young age.

Ibrahim's (peace be upon him) discussion with his father regarding idol worship, as mentioned in Surat Maryam, occurred after his prophethood.

As for his discussion with his people about star worship, as mentioned in Surat Al-An'am, scholars have differed on its timing—whether it was before or after his prophethood. However, the context of the verses suggests that it was after his prophethood, in the context of a debate and establishing proof against his people. Indeed, Ibrahim (peace be upon him) never associated partners with Allah. The Quran clarifies that he was granted wisdom beforehand and that he was a monotheist, not an idolater.