Hi Kevin,
it's been a while since your post here.
I was basically raised as a JW and felt to young for any romantic relationship when I was 17...
not because I liked to... I was totally into a girl which was 3 year younger than me.
But my JW education told me to wait and keep calm until we both were in a age to be married.
This is ridiculous.
The young one need to be able and free to explore their feelings. A 13 year old might be to young to marry... yes... but he or she needs to understand the own feelings... its difficult during puperty, yes... but why not let them explore it?
And the next thing is: yes... the other part of this relationship is not a Jehovas Witness... it is not a official requirement to marry only Jws. But you wont get any support if you do not marry within the organization. You wont get any privileges (because as a brother you cannot be a good head of the family, when the wife is a non JW).
Leave them be... let them make their own experience, just help them stay true to moral principals and the law if necessary.
I wish you guys luck...