The sincere believers will obey the orders of Imam Al-Mahdi (AS) in every matter in their life. He will not order all the believers to fight. His aim is not merely fighting but only against the enemies of human beings who are the tyrants. He will clean the whole earth from tyranny and injustice and fill the whole earth with justice and fairness.
He will never ask people to do any thing which they do not know, so, if you have no experience in fighting, you will not be asked to fight, unless you go through suitable training which makes you able to fight. That also only fighting was required in your area, which is not confirmed in every area. We need to prepare ourselves to obey the orders of our Imam (AS) but we can never know now whether he will order us to fight against the enemies of human beings or to build our societies and serve people.