At age 58, there are 88,792 people alive. At age 62, there are 84,173 people alive. So 88,792 - 84,173 = 4,619 people die over those 4 years. If deaths are uniformly distributed over the 4-year period, then half will occur in the first 2 years (between 58 and 60). So 2,309.5 will die between 58 and 60. This leaves 88,792 - 2,309.5 = 86,482.5 people at age 60.
