I'd put it differently: There's nothing intrinsically wrong with a 16-year-old and a 30-year-old having sex, any more than there is anything intrinsically wrong with two 30-year-olds having sex. There may be extrinsic factors in either case that make it problematic (somebody's being coerced or forced, somebody's elsewhere married, somebody's intoxicated, somebody's being manipulative to get the sex). The way our society is set up, the first case is dramatically more likely to feature such extrinsic factors than the second case.