A militia is an organization, not an individual. Well-regulated organizations have a stated and understood mission, rules as to how that mission will and will not be pursued, and governance that is independent of the execution of that mission.
Thus we have civilian oversight of the military, legislative oversight of the executive as part of checks and balances, boards of directors overseeing corporations and non-profits, etc.
A solitary individual with a gun, no matter how good a person they are, is neither well-regulated nor a militia.
It is common to misunderstand what "well regulated" meant at the time of writing. (It did not mean having "rules" or "governance;" rather, it simply meant "working well" for its purpose. And the "mission" is stated right there: it is to ensure the "security of a free state." One person may not be enough - but it's a start.)
