In order for the central to only initiate connections with a specific device you should use scanning filters on the central so that it filters out any non-target device advertisings, and only attempts to connect if the filter(s) are matched. The peripheral needs to be set up so that its advertisements matches the filter requirements of the central device, and that it advertises as CONNECTABLE.
You could see this demonstrated in some of the ble_peripheral and ble_central examples from the SDK. For instance, take a look at how the Nordic UART central scans for Nordic UART peripheral devices advertising the name NORDIC_UART, and connects to it if found.
