I’m a little late to this party, but as an artist myself, I’d recommend that a young artist learn to embrace saving and investing early. They should start to regularly save and invest a good percentage of their earnings as soon as they earn anything.
In addition, they should be aware of any expenditures for creating their work: the cost of their art materials, the cost for renting a studio when the time comes, etc, and make sure these things are well within their budgets.
I know this isn't the focus of this thread, but in terms of gaining creative skills, I'd recommend a young artist learn to examine people and objects visually. They need to make this a habit.
It’s a good idea to get a lot of experience in different kinds of visual art: nude figure drawing (a must), figure painting, landscape and skill life drawing/painting, abstract drawing/painting, collage, perspective, portraits, human anatomy, mixed media, illustration, graphic design, web design, 3D animation, film shooting and editing.
I’d also recommend studying motion and how objects/bodies move, especially for animation. In addition to the important skill of observing well, a course or two in human anatomy is a good idea for this (or for any artist, actually). Dance, sports, or yoga courses also help to understand movement.
I'd recommend the young artist read well and often, and be trained in writing. At some point they're going to be writing and communicating about their work, so they need good language skills.
They should study art history and constantly look at art in books, galleries, online, etc. They should get input from all the arts, and from other areas as well: music, dance, film, theater, poetry, opera, literature, psychology, science. The inner resources they draw from need to be as rich and deep as possible. They also need to learn how to recognize and avoid cliché.
There are important business skills to acquire: networking, marketing, accounting, entrepreneurship, balancing a budget, how to approach/deal with a gallery, how to get a job in a commercial art field, what demonstrable skills are required. They should keep aware of any available opportunities/courses to learn business skills, whether geared toward artists or not.
They should find a group of like-minded individuals to share ideas with, to give and receive support. Being an artist in a somewhat unaware-of-art world can be challenging, so they’ll benefit from having supportive individuals around them.
To comment on a remark made by another poster: Producing a good illustration/artwork every day can be difficult, for many reasons. I’d say producing a good artwork every week is more than challenging enough. But if the spirit of that post was “work constantly”, I’d agree. The more you paint/draw/design, the better.