Veteran's Rewards are awarded by account age. An additional 90 days is granted for every expansion the account owns through Rise of Kunark. Each Veteran Reward can be claimed once per character. You can see your account age in your Persona Window, in the Details tab.
Find your Veteran's Rewards in your /claim window. These rewards may be claimed once per character.
In the past, there were rewards given for purchasing multi-month subscriptions