Hi Bluebeads.
To put this in context, I'm not and never have been a JW. I have no personal experience of the way the organisation works. So I base this on my understanding as it is.
These are generalisations, but I think many posters would accept them:
1. Elders have a significant degree of authority in their congregations.
2. Because of the emphasis on avoiding 'worldly' contacts, etc., many JWs may be relatively naieve (other than the general perception that everything outside the JW world is evil)
3. JWs are encouraged to keep anything that happens within a congregation quiet, so as to preserve the organisation's reputation.
You obviously found this man's comments and conversation inappropriate. They certainly seem so to me. I entirely agree that you should tell people about it, especially your parents and your friends. You should not be alone with this man. To be honest, if he's in his 60's and trying to 'groom' a 19 year old (and it sounds like that to me) he may not be too worried if his next or other targets are a few years younger.
But I would go further. If, when I was a police officer, I heard about this I would have spoken to my colleagues in the child/family protection unit to see if there was any record of this man. If there wasn't I would have entered the information. If you know any police officers (or social workers or similar) speak to them about it.
I don't know where you are. If you're in the UK or somewhere where they have police family protection units, I'd ask you (if you can) to arrange a confidential talk with them. You don't have to make a statement, complaint or anything formal, just give them the information. It may match up with something they already know or may be a 'heads up'. At least you've done your bit.
I may, of course, be doing this man a disservice and his motives are entirely harmless. Unfortunately too many years of dealing with too many cases suggests that he is a danger to youngsters.