Could a virgin have vaginal prolapse?

Yes: Yes; there are many causes of vaginal prolapse, not all of which require childbirth or sexual activity. Vaginal prolapse is a type of hernia; so if you do things like heavy lifting (>40lbs) regularly, or have significant constipation, the support of the vaginal structures can be affected.

Very unlikely: Prolapse can occur for a number of different reasons -- even if you are a virgin, but it is highly unlikely. If you think you are having symptoms of prolapse, you should be evaluated by a urogynecologist or a gynecologist.

Yes: Although vaginal childbirth is a big risk factor for prolapse, there are other risk factors such as chronic straining from constipation, chronic coughing, or heavy work or anything that increases intra-abdominal pressure. There may be genetic predisposition also.