The longevity of paint on wood depends on factors like the quality of the paint, surface preparation, exposure to elements, and maintenance. Exterior paint on wood surfaces can last 5 to 15 years or more with proper care and maintenance. Interior paint tends to have a longer life span, often 10 years or more. Regular cleaning, touch-ups, and addressing any issues like peeling or cracking can extend the life of the paint. 

You can paint an old wooden fence, but make sure first to do a deep clean (ideally with a pressure washer) and inspect the fence for any existing damage. Painting over dirt and debris will cause your paint to peel. Once you’ve cleaned and repaired any minor issues, use a primer and high-quality satin paint.

Staining pressure-treated wood is a recommended practice. While inherently resilient, it's not impervious to moisture and UV exposure. Staining treated wood is feasible and recommended for enhanced protection and longevity. Applying stain and sealant safeguards against degradation, prolonging its life span. These measures shield the wood from environmental threats while augmenting its aesthetic appeal, ensuring your investment endures the test of time.

Yes, you can and should paint or stain pressure-treated wood to help prevent the boards from cracking. However, you must wait for the wood to dry out completely before applying any finish. Freshly treated wood can take weeks or even months to dry; a common recommendation is to wait three to six months. To check if the wood is ready, perform a simple water test: drip some water onto the surface. If the water beads up, the wood is still too wet and needs more time to dry. If the wood absorbs the water, it is dry enough to be painted or stained. You can proceed with building your deck or fence while the wood is still wet, but you will need to wait to apply the paint or stain.