I really dislike the phrase "failure to launch". They're not failures, they're not defective machines. They're people who, at least in part, are choosing not to have sex or be in a relationship. And if they aren't doing it by choice, then it most definitely isn't their responsibility for not "launching" into the roles they are expected to conform to.
Strange but true: Being in a romantic relationship is not a requirement to be a valid or great human being.