Bitcoin millionaire speaks at a TEDx Teen conference back in 2014. Erik Finman Erik Finman may be only 18, but he's a millionaire, thanks to a very shrewd and early investment in bitcoin.

And despite the recent tumult in the world of digital currency and a huge run-up in the value of bitcoin, Finman is still a bitcoin believer. By his reckoning, the cyber currency still has a ton of upside.

Indeed, Finman said recently that buying bitcoin now would be a "very smart financial decision."

The teen mogul is putting his money where his mouth is. He owns 403 bitcoins, which give him a net worth of around $1.7 million. He's not going to college, and he doesn't have a steady job. He's just focusing on his bitcoin investments. Well, that and launching a satellite stocked with a signed Taylor Swift CD into low-earth orbit.

His faith in bitcoin hasn't been shaken by recent events, such as the explosive growth of Ethereum, a rival digital currency system, the "hard fork" to bitcoin that divided the market for the currency, or the big rise in the value of bitcoin. Each coin is now worth more than $4,300, up from less than $1,000 each as recently as March.

While there will be some "ups and downs" to bitcoin in the near future, Finman expects that it could go up "much, much, much more" — possibly to as high as $10,000 per coin.

The alternatives

Finman doesn't pay much mind to cyber currency alternatives like bitcoin cash, a currency that spun off from bitcoin following a schism within the bitcoin community. Finman sees it as an "alt-coin;" an offshoot that's more of a minor experiment than a true successor to bitcoin itself.

Finman's also skeptical of Ethereum, which has been getting a lot of traction in Silicon Valley. Each ether — Ethereum's name for its digital coins — is now worth $300, and proponents see unlimited upside.

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But Finman believes that growth in Ethereum is being driven largely by speculators who are creating a bubble that could burst one day. In the bitcoin community, Ethereum is sometimes known as "Ponzi-coin," he said, a characterization that he "might agree with."

There's "a lot of money short-term" to be made with Ethereum, he said, but he's unconvinced of its long-term viability as a true digital currency.

He feels similarly about initial coin offerings, or ICOs, where companies are launching new currencies or digital tokens by exchanging them for bitcoin or ether. He thinks ICOs are "cool and innovative" in theory, but describes much of the execution as "Gordon Gekko-esque" — referencing the unethically greedy antihero from the "Wall Street" movies — insofar as they're largely unregulated and highly risky for investors.