Can I go off shore fishing if the charter boat does not exceed the U.S. territorial waters ?

I wouldn't take the word of anything you find online...the consequences would be too great to take the risk, In my humble opinion, because you should be asking the people you report to. Their answer carries weight... "but I read it online" isn't going to be an acceptable excuse if they would prohibit it.

An overabundence of caution is in order.