Today times, there's the internet options: Youtubers, game streaming, digital sports, even webcam sex (well, might not be legal for your age bracket, but can always be sidestepped one way or another), and, of course, apps and programming in general (teen prodigies are still a thing) and even hacking, dark web deals, bitcoin schemes and scams...
So, yeah, for a change they may "find treasure" in the virtual economy.
Hey, let's say, they sell MMORPG accounts. They're both veterans of a super popular game, and have close to maxed out their main accounts, and run a bunch of side ones for cheating and fun. Perhaps, they have written or gathered some scripts that let them automate mundane tasks meant to force players either invest insane time or spend money for boosters. Yes it's illegal, but popular and active battlefield. So they are able to quickly build up a bunch of accounts for sale in black market (selling/transfering accounts is against rules, but almost nothing can be done to prevent it in practice). The cash can be surprisingly huge in those deals, and with some artistic license, almost whatever you want.
Once they have the farm... yes, there gonna be regional specifics, but generally I tend to agree with above, making farm profitable is a hard task usually requiring operation at scale, at least as far traditional products are considered.
So, they aren't dealing with traditional products, most likely. They either use the farm just as base camp for completely different activities, be it their digital exploits or some form of craftsmanship or services (again, even if it's nominally illegal, services in place paid in cash, should be doable in most cases), or something else using the property itself, be it some tourist attraction, or hosting events, maybe they open a paintball park or something.
In most cases when it's an official business (even the farm itself?) they probably need a front person, adult who makes the documents seem right, even if their real involvement is minimal.
Using the land, it's probably some exotic produce, pharmaceutical plants for example, or for more traditional, some high value "biological" farming, but that needs direct market with upper class city dwellers and is more "European" thingy perhaps.
Beekeeping is a great option. It requires some solid knowledge, but isn't as complex as it is made to appear, at least at starting levels, and should be easily accessible for high intelligence characters capable of systemic thinking. It's one way to have high value on a relatively small piece of land, in the borderline case only land under the apiary itself, harvesting nectar from neighboring properties (up to 3 miles around, next to unlimited range with traveling apiary); formal agreements of pollination with orchard and field owners may be sought and profited from (local specifics may apply).
Apiary starting from scratch is relatively inexpensive, it may be just a handful hives and already generate small profits, and grow very fast at the same time, in practice, 2 to 4 times every year (in theory even much faster) up to the desired size that depend mostly on environment factors (some wilderness in range is highly beneficial and perhaps required) it can be managed alone (for a fast estimate, up to around 100 hives per beekeeper working full time), although nominally it's at the minimum master beekeeper and a helper for professional operation of 150-400 hives.
There's a lot larger spectrum of production than just honey, and it also plays well with what I mentioned above: if there's specifically nectar fields they might be as well also plants with special value, and apitherapy is also increasingly a tourist attraction, including real and "new age" bordering services; even sleeping on beehives is a thing.