Catherine-middleton.com has been registered since 2015, so it isn't a brand-new domain trying to disappear after a week. But age alone isn't trust. This site provides almost nothing that would let a visitor understand who runs it or why it exists. There's no about page, no contact email or phone number, and no privacy policy or terms of service. For a personal blog or hobby site, some of those omissions would be normal, but even hobbyists usually say who they are somewhere.
The technical setup is fine — modern encryption, clean security scans, a decade of web archive history. The problem is that the owner has gone out of their way to stay invisible: the WHOIS registration is private, the homepage shows no useful text, and the site actively blocks automated checks. When a site that old still won't tell you anything about itself, the safest assumption is that it doesn't want to be held accountable. If you're wondering 'is catherine-middleton.com a scam,' there's not enough evidence to call it one outright — but there's also not enough evidence to call it anything else. Pass on this one.