Our Earth is almost 4.5 billion years old. Very few things existed then that we still see today. Probably the oldest available resource on Earth was the sunlight. Since Sun is older than Earth, we can see why sunlight is the oldest available resource to us. Wind is also among the oldest resources. Water was initially in the form of vapors and converted to liquid form later and thus was not available initially. Many of our rocks and elements have been formed by geological processes over a long period of time and thus contain a number of rocks and minerals which are relatively new. Fossil fuels were only formed after life evolved on Earth and thus are fairly recent.
In short, the oldest available resources (probably as old as the Earth itself) are sunlight and wind.