Yes, there are rules associated with selling alcohol on eBay - see the ebay alcohol policy for more info.
You will need to add to every listing a disclaimer supporting the responsible service of alcohol or whatever the regulations are for the states you sell into. e.g We support the Responsible Service of Alcohol. New South Wales: Liquor Act 2007. It is against the law to sell or supply alcohol to, or to obtain alcohol on behalf of, a person under the age of 18 years.
To add this to every product listing go to 'Settings - Feeds - Description Template' and add the disclaimer here. It will be applied to every product that you list on eBay. If you only need it on a specific product, go to 'Inventory - All products' Find the product then on the full product details page click edit. Scroll down to 'detailed description' and enter the disclaimer here.