Finding version (compatibility) of current .ai document

you can select the file in Bridge and look at the Application property in the Metadata panel

and taken from majorLaser's on this post http://forums.adobe.com/message/2036802#2036802

#target illustrator
//To use the XMP objects, you must load the XMP library as an ExtendScript ExternalObject. To avoid
//loading multiple instances of the library, use code like the following:
// load the library
if (ExternalObject.AdobeXMPScript == undefined) {
ExternalObject.AdobeXMPScript = new
ExternalObject("lib:AdobeXMPScript");
}
//Create an XMPMeta object from the active documents XMPString:
var myXmp = new XMPMeta(app.activeDocument.XMPString);
 // retrieve property
prop = myXmp.getProperty(XMPConst.NS_XMP, "CreatorTool");
alert("Document Created in " + prop);