I would advocate some college education if this person wants to be successfully self employed. Unless he/she has entrepreneurial parents willing to provide business coaching (and the 18 yo is willing to listen to them), some advanced business training would be useful for a photography job and and any other future employment.
Perhaps an associate degree at a local state university branch or community college. 4-year degrees are nice but not necessary, and many people do not use their 4 year degrees, changing plans after college. Thus the investment in a 4 year degree is often "wasted", despite the value of what they learned, because it wasn't applied to their job.
A "trade" job like plumber, photographer, metal fabricator can make decent money on their own, but it won't happen well if the person has no business skills or training. If they work for someone else, their motive should certainly not be a comfortable income. A spouse with business skills could also complement the trade person's trade skills, but I think it's better if one person can grasp both aspect of self employment.
There are plenty of good business people who are weak on photography skill as well. The 18yo should continue to refine their photography skills and enjoy all aspects of photography such as digital, analog, darkroom, computer skills, lighting, etc...