As we read in Dua e Ahad that raise us along with our Imam. So first, at what age will we be revived? Second we say that take me out of my grave using my shroud as dress, so a person who knows to fight will only be able to fight or even other would be able to fight because of spirituality? Third in dua we say (walmustashhadina bayna yadayhi) and those who will be martyred before him. what does this line means?

Your first question about age, the answer is related to 2nd question as person comes with Kafan means that age he died, but after that he got powers or anything happens.
The Dress is sign of good deeds in person life, i.e Taqwa, so person fights with spiritual powers but it doesn't mean that we don't have to be active physically in our present life.
Related to Shadat are those who martyred before reappearance of Imam e Zaman ajtf also having a place , but we pray that we want Shahadat in his hands or in his army.