The bottom line.... Underage is illegal. Against the law regardless of the "cultural norms" of the JW cult.
The conversation keeps equivocating on this point. Is the issue the law, in which case you have to consider the location of the OP and whether the young lady was 16 or 15, or is the issue what is acceptable, normal, and not creepy?
I think the pertinent issue is the creepy factor. When the law is brought up, you have to be willing to accept that US law on such things as alcohol consumption, gun ownership, or the age of consent (which varies by state, anyway) is not somehow the moral yardstick for the rest of humanity. America is pretty damn important, but not THAT important.