No, you are not a fraud.
Due to how young gaming is, in relation to other forms of entertainment, we can still see a lot of people, like Jeff, that have experience with the hobby as a whole, however the idea that you have to have an all-encompassing experience to be a legitimate fan of something is ridiculous. You do not have to watch every single movie to consider yourself a movie buff, the same goes for books or music.
However in all art forms exists the idea of the Classic, a seminal work that is seen as incredibly influential to the form as a whole. In gaming there are several of Classics, many made by Nintendo, going back and experiencing them is worthwhile, but you have to set your expectations accordingly.
I subscribe to what Rorie said on the last live stream of the year. Gaming is getting continuously better, and games coming out now are better than those of old, so going back to, as Jeff put it, “The Old Shit” can be a frustrating and depressing experience.
EDIT: can't remember if Rorie said that on the last live stream or on the last regular Bombcast.