  This paper examines the average age minimization problem where only a
fraction of the network users can transmit simultaneously over unreliable
channels. Finding the optimal scheduling scheme, in this case, is known to be
challenging. Accordingly, the Whittle's index policy was proposed in the
literature as a low-complexity heuristic to the problem. Although simple to
implement, characterizing this policy's performance is recognized to be a
notoriously tricky task. In the sequel, we provide a new mathematical approach
to establish its optimality in the many-users regime for specific network
settings. Our novel approach is based on intricate techniques, and unlike
previous works in the literature, it is free of any mathematical assumptions.
These findings showcase that the Whittle's index policy has analytically
provable asymptotic optimality for the AoI minimization problem. Finally, we
lay out numerical results that corroborate our theoretical findings and
demonstrate the policy's notable performance in the many-users regime.
