It's actually very easy to be able to call yourself a detective in the traditional sense of a "private eye." Most states barely have any requirements aside from applying for a license.
Whether or not you'll be any good at it, or get any clients is another story. It's such a romantic job, there are probably a fair amount of people out there calling themselves detectives. And quite a few of those people have real police experience and know what they're doing.
I can see how a young person might think they have what it takes because they're good at looking things up online, but almost everyone is these days. Becoming a real detective would take contacts and experience and even then I think it would be difficult to drum up a client list, because, let's face it, how many people actually need a detective at any point?