I knew a guy in high school who was around 16 or 17 and was dating a woman in her late 20's/early 30's and his mom nailed her for statutory rape and even got a restraining order against her. Did it adversly effect him? I don't think so. After they broke up he started going out with a girl who was a grade lower than us and they were together for years. None of them were JW's though.
As for myself, 21 year old JW girl and 23 year old JW girl with 16 year old JW boy, doing naughty things together, no problem what so ever. Never told any of the elders or anything like that but bragged like crazy to various friends. I doubt they really cared about emotional issues or anything like that but then again, its not exactly like I was into their minds or anything. Did it harm me in any way? Nope. If I went back and had the chance to walk away instead there's no way I would, too many good memories!!!!
Now as for non-JW age differences, one of my friend's (as in female friend who I messed around with some) mom came onto me, heavily, once when she was drunk when I just turned 15. I didn't do it because I thought it was kind of creeepy but I'm not traumatized or anything. Also, when I was 15 I went out with an 18 year old who introduced me into many different things and I'm not hurt by it at all. In fact, I'm thankful. Every girlfriend I've had since her has bennifitted from what she taught me. True, at times I was slightly confused but when you're learning stuff, especially something so enjoyable, you usually don't pick it up right away and get slightly confused with it. Once again, I'd gladly do it all over again. On the flip side, when I was 17/18 I went out with a 14/15 year old girl and did quite a bit of naughty stuff with her. I don't really think it effected her negatively and I sure as hell didn't have any negative side effects from it.
Personally, I think more damage can occur just with an emotional relationship instead of a physical one. The two times when I was really messed up from a relationship and very negatively effected was with two girls I never slept with (well, I messed around with one of them but it was long after I had gotten over her and we both knew it was just physical which was just fine). One of them I kissed once and I was a wreck for months when we split because of the emotional attachment was there. The other girl, we came pretty close but never did (not because I didn't want to though) and when we split I was messed up for a year or two. If you really want to stop damage try to keep your boys from getting in tangled emotional relationships until they can handle it. I know personaly those were the ones that caused far more damage than the physical ones.