If you create content on Youtube, watch people who create content on Youtube, if you interact with people on Youtube via comments or other social networks, if you have a connection to people on the website, then you are part of the Youtube community, and therefore, a youtuber.
"To me, a YouTuber is someone who part of the community of people that actually cares about YouTube and the creations that it hosts."- Hank Green
A "youtuber" is simply one participating in watching Youtube videos. The amount of videos watched or uploaded by the youtuber is irrelevant. A person swimming for the first time in their life is still a "swimmer" at that moment in time, regardless of their experience. They might be a bad swimmer, but a swimmer nonetheless.
"Davis is watching a Youtube video. Davis is a youtuber."