Is it obligatory to conduct all aspects of life and calculate ages using the Arabic months, and is dealing with the Gregorian months considered a sin?

The Arabs used to follow the lunar calendar based on the visual sighting of the crescent moon. The Qur'an affirmed that the number of months is twelve, four of which are sacred. 'Umar ibn al-Khattab established the Hijri calendar, which is based on lunar months, upon the consultation of the Companions. They chose it to differ from the polytheists and to distinguish the Muslim nation. All religious obligations, such as fasting, zakat, and Hajj, are tied to the lunar months, while solar months are associated with agricultural and climatic seasons. It is preferable to use lunar months in transactions, but there is no harm in using solar months when needed.