Can I benefit from taking a multivitamin, as a somewhat active 19 year old male?

Yes. Multivitamins are "supplements" and are meant to be something extra you would take in addition to your healthy diet. However, we don't always eat a healthy diet, or we may be ill and not have much of an appetite. When this occurs, the multivitamin can be an adjunct to the nutrients we get from foods. Multivitamins are like insurance; you hope you never need to use it but it's available if needed.