Every single person's age is fixed. It cannot increase from it's fixed time nor can it decrease. When the time of life is finishing, Hazrat Izraeel Alaihi Salaam comes to extract the dying person's soul, and the person dying looks to his left and right and sees Angels everywhere. The angels of mercy come to a Muslim and for the infidels the angels of punishment appear. At this time even the infidels believe the truth about Islam, but their faith is at this time is not counted. This is because faith is the name of believing the message of Allah and his beloved Messenger without seeing proof, and at this time one sees the angels and then believes and this is therefore not accepted as a Muslim. A Muslim's soul is taken out with ease and is then taken with respect by the angels of mercy. An infidel's soul is taken out with great pain and the angels of punishment take it with disgrace. After death the soul does not go into another body and is then reborn, but upto the day of judgement stays in the world of 'barzakh' meaning the interval between death and resurrection. To believe that the soul goes into another human body or an animal's body or into trees or plants etc. and is known as reincarnation is wrong and is Kufr.