I think the age of the domain definitely helps if it's an older domain, but could work against for newer domains. Maybe show by default, and do not show on a domain basis (as an option). As for domain length, don't think it's necessary to show, although it wouldn't be harmful. A buyer looking for short domains already knows how many characters a domain has. And someone looking for a brandable or keyword domain, isn't really going to care how long the domain is.