What do you think? Is it a loophole?
Maybe, but only if you annul your membership immediately after reaching the age of majority.
Under normal contract law (if I remember correctly from Business Law 101 and 102), a minor who enters into a contract can annul that contract. However, if he continues to act under that contract after attaining the age of majority (say, by making payments on an installment purchase), then he has affirmed the contract as an adult, and is bound by it just as if he had been an adult when he entered into it.
So, applying this to the JW thing, it is conceivable that one baptized as a minor might be able to annul his baptism up to the time of his reaching majority. For example, if you were baptized at 12, and 18 is the age of majority in your area, you could annul your baptism under this theory up until your 18th birthday, or within a reasonable time thereafter, provided you had not acted as one of Jehovah's Witnesses after turning 18.
What might constitute "acting as one of Jehovah's Witnesses"? I suspect that one could make the argument that attending meetings is not sufficient in itself, since meeting attendance is essentially a passive pursuit, but engaging in and reporting field service almost certainly would. Likewise giving parts on a meeting or helping out at a quick-build project.
The problem with all this is that these are procedures that might reasonably be expected to be followed in a court of law. The JW's have their own law, and any legal argument you might make of this sort isn't likely to affect their shunning policy toward you. It might, however, help to use this sort of reasoning if you were actually involved in litigation over a disfellowshipping.
But then, I'm not a lawyer; I could be wrong...
Tom
"The truth was obscure, too profound and too pure; to live it you had to explode." ---Bob Dylan