Pay attention to your gates. If they start to drag, this can cause issues the strutual integrity of the gate. A simple fix if caught early can save you from having to replace your gate in the near future.
Things to look for with your aging fence.
Be careful not to pile mulch up to your fence. This can allow build up of organic material against your fence and cause it to prematurely rot out.
Also, this can block the natural flow of water casing flooding on your's or your neighbor's property.
Do not lean heavy items against your fence. Doing so can cause warping of the lumber.
Staining/sealing can help extend the life of your fence. Pay attention to the frequency rate on how often this should be done in your area. This will help maintain the fence as it ages.