I think there's also a couple of distinctions to make here. While some people on YouTube are looking to build on that into traditional fame in movies, tv, recordings, whatever, there's far more who have no desire for traditional fame - only a creative outlet while they enjoy their "regular" civilian lives.
There are a range of motivations that lead individuals to create for YouTube (as opposed to those who simply use YT as a place to post home videos). I believe that a large majority (though certainly not everyone) fall roughly into three major categories.
Some, as Ken suggests, enjoy YT strictly as a creative outlet. Subscriptions and a YT "career" aren't a priority or even a consideration. Regardless, some of this group might reach a level of recognition (perhaps including what might be called "fame") - and may in fact include the best and most creative of those referred to as YouTube "stars." Sometimes, if you enjoy what you're doing, your audience enjoys it, too. This group is probably the most diverse in terms of age, from the youngest to the oldest users, and generally include the majority of vloggers, artists and musicians.
Others hope to use this world as both a place to build YT fame and as springboard to wider fame - these celebrity culture addicts, perhaps, see YouTube as the best "shortcut"available. They might have a level of skill in music or comedy, but their motivations are based more on growing a following than developing their craft or a quality video "product." They might, in fact, succeed working the system to reach a level of visibility and even limited "stardom" for a while, but like any of those who seek fame for fame's sake, that sort of goal could lead, inevitably, to personal disaster. At the very least, they're the sort of YouTubers with a huge following, but few actual per-video views. If you actually see their videos, you're likely to scratch your head and wonder why.
There's also a lively third group that looks at YouTube and the social media environment as both a means of expression, and as a platform offering an ideal foundation on which to build their creative future. They're not looking at achieving fame necessarily - but at using the overall social media platform as an opportunity. This category can overlap quite effectively with the first category - perhaps consisting of the best of the social media / YouTube entrepreneurs.
There are, of course countless sub-groups and fringe categories that make up the YouTube world - but I'd like to hear your opinion - are these fair definitions?