I had heard pressure treated lumber is not safe for areas where food is grown. I suppose in your case along the driveway and lawn it's okay to use.

Is pressure treated wood safe for vegetable gardens?Even though the new pressure-treated woods are considered safe, Wolmanized Outdoor, according to its Web site, does not recommend using pressure-treated wood where the preservatives may become a component of food. Its recommendation is to use an impervious liner between the wood and the soil.

https://www.finegardening.com/article/are-pressure-treated-woods-safe-in-garden-beds#:~:text=Even%20though%20the%20new%20pressure,the%20wood%20and%20the%20soil.

To answer the OP:s question, as long as the untreated wood is not subject to continually moist/wet conditions, it should easily last 10-15 years. This situation poses no issue to any edible crops anyway.

And I'm not sure that quote about the potential of pressure treated wood contaminating food crops is particularly accurate. It sounds like they are referencing the old PT, which had all kinds of safety and contamination issues but has been off the market since 2004. Nearly all current PT lumber is treated with ACQ (alkaline copper quaternary) or CA (copper azole), neither of which pose any serious toxicity nor the likelihood of being absorbed in any quantity by plant tissues. This has been documented by the EPA, the American Wood Protection Association and the Health Canada Pest Management Regulatory Agency (PMRA).