You can eat 20 year old sugar as sugar lasts basically forever although the sugar as it ages can become hard and clump up.
If the sugar has gone hard you can break it up and it will still dissolve in liquids such as tea, juice etc.
You can also use the 20 year old or hard sugar in baked goods or anything else you want to use it in.
As long as there's no bugs or anything else bad in the sugar it's safe to use the old sugar.
Sugar does not expire although over time the sugar can start to harden and clump up when it is affected by moisture.
As the sugar absorbs moisture it can become hard but it does not go bad in that it will make you sick.
If you have sugar that goes hard you can break it up and still use it in tea, drinks, foods etc.
Sugar is best used within 2 years of purchasing the sugar but it will remain safe for many years even after it has hardened.
In reality sugar has an indefinite shelf life that doesn't technically expire but will degrade in quality over time.
If sugar sits in your cupboard or pantry for too long, it is likely to crystalize and harden.
The color and flavor of the sugar can change too, so it is recommended to use sugar within two years.
Sugar has a best-if-used by date of approximately 2 years for quality concerns.
This is due to lumpiness or hardening in granulated sugars and crystallization of sugars in honey and syrup.
It is still safe to use even when lumpy or crystals are present.