Many gardeners prefer untreated wood for vegetable gardens. Cedar and redwood are naturally rot-resistant.

depending on where you live a few year’s

or you could go with

Landscape ‘timbers.’ These are made from recycled plastic, weather well and last a long time. Some are even manufactured to look like weathered wood.
or
Decorative concrete block or stones. Blocks and stones are usually used to build retaining walls but also make excellent raised bed frames. They’re durable, and you can stack them to varying heights to make tiered beds.