Old compost = soil, the carbon value to your soil will be the same as will most other nutriments if rain has not leached them out.

It probably depends what your compost is made from, but I have never had a problem with using old compost.

My grandfather used horse manure on his gardens. He said it was never good until it had aged several years. Overall, compost is good for your garden, but it can also have a short term negative effect of binding up nitrogen. I don't recall the details, but nitrogen generally needs to be "fixed" into a form that plants can use. Legumes are good for this fixing of nitrogen. I just remember being advised by a horticulturalist to mix a nitrogen fertilizer when using compost on tbe garden.

When I get too old I turn into compost.

It only loses its potency if it has been leached out by heavy rains or flooding. Otherwise the nutritional value stays in the soil for a long time. It gets used up by the plants and then goes back into the soil when the plants are composted.again. Minerals, nutrients and chemicals all get used many times. Nitrogen and carbon are the most important.

Older the better

I have had the same compost heap for the last 15 years, you just keep adding to it, I recycle my old soil from my pots. That allows you to mix old and new together. Just keep adding more organic matter, the different levels of decomposition release nutrients in a slow release format.

Thanks everybody

Part of the point of compost is nutrients, but part is the structure it adds to soil. That latter part remains worthwhile, even old. The former can be rejuvenated by adding some fresh organic matter.

You want stuff to be completely broken down. Depending on what you put into it this could take at least a year often longer. I sometimes keep it wet and, in the winter, cover it with a piece of burlap.

It will be fine, perhaps even better