It can be, but remember that you can work as hard as you possibly can and still never make YouTube a sustainable career. It'll all depend on what content people want, and other things like that. Plus, there are a ton of people that want the exact same thing as you, and are trying as hard as they can to get it, so I can't say it will be easy -- but it's certainly possible!
Besides, I think you'd have to rely on a little more than YouTube, anyway. For example, from what I've seen, animators can't solely make a living from YouTube due to how long the animation process takes them. They rely on fan funding, donations, art commissions, merchandise, and likely many other things to actually make things work out. YouTube, by itself, may not be a good idea even if you receive millions of views a month.