He wants to pray to Allah to let him live until he witnesses the descent of ‘Eesa (peace be upon him) at the end of time
What appears to be the case is that it is not appropriate to pray to live long enough to witness the descent of ‘Eesa and see the signs that will occur at that time. Rather each of us should ask his Lord to give him a long life of obedience to Him and enable him to do righteous deeds, and let the end of his life come when he is doing such deeds.
For more information, please see the answer to question no. 41017.
With regard to strengthening one’s faith, that may be achieved by doing acts of worship and righteous deeds, keeping away from sin and those who commit it, love of dhikr and Qur’an, and focusing on doing that which is right and proper.
For more information on ways of strengthening faith, please see the answer to question 223615.
And Allah knows best.