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This paper proposes an age artificial immune system (AAIS), for optimal order pickings in an Automated Storage and Retrieval System (AS/RS) with multiple input/ output stations. A mathematical model is presented to describe the characteristics of the AS/RS. It is optimized with the proposed algorithm, which is based on the clonal selection principle and the aging concept. Unlike conventional algorithms for artificial immune systems, the proposed algorithm consists of antibodies whose abilities to be cloned and to survive depend on their ages, and adopts a mutation scheme based on randomized rankings. To further improve the performance of AAIS, a crossover operator is also included in the algorithm to form the AAIS-CX algorithm. The performance of both algorithms is tested with the problems of optimal order pickings in an AS/RS with multiple input/output stations. Comparison of the results obtained by using AAIS-CX, AAIS, the techniques of nearest neighbor heuristics, genetic algorithms and ant colony systems clearly shows that AAIS-CX is superior to the other algorithms. Suggestions for future work are also included [ABSTRACT FROM AUTHOR]