TL;DR an evil institution forces its monopoly on contract enforcement and then uses its position to "protect" people from themselves. Cryptocurrencies bring the end to that.
Minors can't run a business, contract, work full-time, even use many websites, and do a great deal of other things because...
the State wishes to protect them from
the dangers of voluntary excha themselves.
As someone who has a first-hands experience with the issue, I can tell that these things anything but protect me. This post, however, focuses on a general problem, not my personal experiences with it.
Why can't everyone contract?
But first, let's step out for a moment. On a higher level, there got to be a cause for this, right? Well, sort of. The idea is that humans aren't capable of reason and taking on responsibility since their birth. Correct? Pretty, yeah.
And why is it important? Because ultimately, contracts need to be enforced, and clearly you can't enforce a contract when one of the parties doesn't understand, and for that matter, is incapable of understanding what's going on.
Also, as one of the parties who enters the contract, you want to be sure that the contract will be enforceable.
What's wrong, then?
Briefly, two things: the State monopoly on enforcement and the State's desire to "protect" everyone.
Why age? It is assumed that reaching the "X years in this life" milestone makes a dummy kid a responsible adult capable of reason, all overnight. It's a rather weird one-size-fits-all solution which doesn't work in some (or many?) cases...
Which is made even worse by the fact that the State grants itself the territorial monopoly on contract enforcement, effectively rendering impossible all alternative non-State arbitrators with their own "responsibility" criteria.
What's even worse is that, once it does have that kind of monopoly, it can begin "protecting" people who didn't even ask for it. For example it can rule that operating a business being a "minor", or making any kind of a contract involving a "minor", is a crime, even if the "minor" in question is a) capable of reason and understanding, b) understand what the contract is implying, c) voluntarily agrees to it.
If a tree falls in a forest and no one is around to hear it, it does make a sound, it's just that nobody knows it did
Luckily, you can circumvent that. If both parties do agree that the State is an undesirable arbitrator, and instead agree to abide by some other arbitrator, then all is fine... As long as the State has no knowledge of the transaction.
Ultimately then, peaceful voluntary transactions not limited by idiosyncrasies of the evil State are possible if there is no way for the State to learn about them.
That is where cryptocurrencies and smart contracts enter the stage. Cryptocurrencies facilitate transactions that would otherwise be impossible because of the government control of banking, and enable arbitration by agreed-upon third parties. (This includes not only "minors" doing business, but also other kinds of voluntary transactions, such as operating a taxi-like service without a medallion, selling marijuana, etc.) Smart contracts (Ethereum seems promising) allow to step even further, removing the need of human arbiters and replacing them with a program. They can be simple, like escrow transactions, or they can be very sophisticated, like a Decentralized Autonomous Organizations.
Widespread adoption of cryptocurrencies for all kinds of transaction, eventually followed by alternative contract enforcement means, is going to shake the State.
The fall of the State's control of money and its monopoly on contract enforcement is around the corner. Abolition of the State isn't far from that. Personally, I couldn't be more excited.