There were several red flags about hiring these specific developers but age is also an important one. When you do business with millions of $, you go with the safe options. The conventional knowledge about software development is that to become a senior developer you need around 10 years of hands on experience. University doesn't count as business experience. At 25 you're fresh off university and you may have one or two years of business experience at best. You're nowhere near a senior developer.
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There are exceptions of course. For instance, Linus Tolvards, the Benevolent Dictator for Life of Linux, started work on the project when he was 21. Similar story for Vitalik Buterin. Hell, even Theymos is a profoundly talented individual because going by his word where he said
he's 21 around 12 years ago. Which means he coded the first ever block explorer when he was a teenager.
So to an extent, maybe we can excuse Theymos for entrusting people around his age. But as I wrote above, when doing business with millions, the safe solution would be to hire an experienced firm, instead of expecting three young adults to show profound levels of intellect and complete a vast project on their own.
I think this idea that because you are 25 years old, you are not capable of leading and carrying out big projects is a big mistake. In fact, it is because of this that a generation of young people lost opportunities in their lives, especially for those who had this idea in the late 90s, early 2000s.
Yes, you gave two exceptions, but in the computer world, there are "many exceptions":
Bill Gates founded Microsoft when he was 19, and his friend Paul Allen was even younger. They didn't even finish college. And the business became worth millions.
Steve Jobs was 21 years old when he created Apple. And Mark Zuckerberg was 19 when he created Facebook.
We don't even know how old Satoshi is, he could have been a 15 year old "kid".
Finally, there are many success stories of young people under 25 who have managed to create companies/businesses worth millions. The issue is not age, but the attitude demonstrated towards a (big) project. Besides, it's easy to point fingers now, but if everything had gone well, they would have been said to be the best choice in the "world": young entrepreneurs.
Yes, there may have been a casting mistake, as even million-dollar companies make. But that had nothing to do with people's ages. It is true that having older people can bring wisdom and experience to projects that is very different from young people, and can provide greater guarantees and stability. But this does not guarantee that the project will be successful, as there are also many stories of older people who failed when leading million-dollar projects.