(I take it you're being sarcastic, and thus I shall try to explain more clearly.)
The OP made an argument of this form:
"I dislike the government asserting that I am not a fully competent adult, capable of making my own decisions about what agreements I enter into and which I do not.
If I'm not competent to read a <contract of form X> and agree, or not agree, to it, then why do they think that I'm competent to drive a car, or vote, or sign a lease?"
The reply by toby noted "You can't sell yourself into slavery" by way of pointing out that the argument does not hold when X = selling yourself into slavery.
Thus toby was demonstrating the OP's argument was not valid as it stands for all forms of contract X, and so it needs to be clarified to indicate why it is valid for X = non-compete agreement (for example by reframing the argument from one based on competence to: "I don't believe the state should refuse to enforce contracts merely on economic grounds")