Parent poster meant "properly cared for timber", not chemically-treated timber. Timber doesn't have an expiration date. As long as you keep it dry, it will last indefinitely. In fact, it becomes stronger over time. There are many 100+ years timber buildings in US.

For timber used outdoors, e.g. for making decks pressure-treated timber is used. It's a timber treated with pesticide (chromated copper arsenate). In the past creosote was used to treat things like wooden railroad ties and power poles, but it's no longer used because it's toxic.