When did Islam start

Islam began with the beginning of the Prophet's mission, when Jibraa'eel (the Archangel Gabriel) brought down the Revelation from Allah in Makkah (Mecca) in the Arabian Peninsula. This occurred on a Monday in the month of Ramadaan, in the fortieth year of the Prophet Muhammad's (peace and blessings of Allah be upon him) life, thirteen years before his Hijrah (migration) to Madeenah (which marks the beginning of the Islamic or Hijri calendar). According to the Gregorian calendar, the beginning of the Prophetic mission happened around 608 or 609 CE. Salmaan al-Farsi, may Allah be pleased with him, one of the Companions of the Prophet (peace and blessings of Allah be upon him) reported that between Muhammad (peace and blessings of Allah be upon him) and Jesus (peace and blessings of Allah be upon him), there were six hundred years.

And Allah knows best.