While the new Lumia Amber update is available only on new Lumia devices such as the Lumia 925 and Lumia 1020, Nokia has confirmed that they have begun to roll out the update for older Lumia Windows Phone 8 devices. However, the actual availability depends on respective markets.
For example, here is the current status of Amber update for Nokia Lumia WP8 devices in Malaysia as detailed by the company:
The Nokia Lumia Amber update is said to bring a number of improvements such as enhanced camera capability, Nokia Smart Camera, Nokia Pro Camera, Nokia Glance Screen, Storage Check and FM radio. Check out www.nokia.com to learn more about it.
[Source: Nokia Conversations]