In any other religion, I would say "no big deal" as to the age.
However, with Jehovah's Witnesses, baptism is more of a contract and a signing away your right to think and choose for yourself. I was baptised at the age of 12, but it was in the good old days before the WTS included that little phrase that locked you into their cult organized religion. My baptism was in the name of the Father, the Son, and the Holy Spirit.
Therefore, since their conditions of baptism have all the ramifications of a contract, you should be at least 18, imo. And, regardless of what others have said about legal recourse, I think you would definitely have a case against them, but would have to find a very very brave and savvy attorney that is able to think outside the box.
Times are changing, and it's time someone stood up for children that make promises or enter a "contract" that they may not have the ability to keep. Losing their entire family for such a mistake is unconscionable.
In my own family, my brother (who was child baptised) got abandoned and shunned by some family members when he got df'd at the age of 17. It devastated him. Another family member raised in it by uber theocratic parents but never baptised (although coerced) is still included in family fun and is shown love and respect.