​​We are looking at large populations of items. Items in populations studies are organisms of the same kind that are born and die. Items considered in reliability context are manufactured, continuously inserted into operation and fail. Our study is the first in the literature to apply methodology of populations dynamics to manufactured items. Stochastic properties of the remaining lifetimes of items with random initial age are investigated. The corresponding equilibrium distribution is defined and analyzed. Various stochastic comparisons between the age and the remaining lifetime for populations of items are obtained and discussed. Some examples for populations of organisms and manufactured items are considered. ​