I encourage you to use the resources I gave you above, and combined with your research and what you know about him already, I hope you will find the best course of action. Being convicted of a crime that is sex-related can cause an automatic, mandatory registration into the sex offender database.When he was 16, he was high on ecstasy and trying to complete a paper for high school when his nephew was bugging him.
I understand that this is not always an easy task, and you may not find out immediately.
To do so, please look at the US Department of Justice Dru Sjodin National Sex Offender Public Website.
When you find out where he was convicted, you can call the court or the local police that handled his case.
I am really concerned and conflicted here on whether I should further invest myself in this person's life or if there are serious red flags that I am being naiive around.
I really need to talk to someone about this and find some proper direction.