Vacationing with girlfriend

My son is 16 years old and so is his girlfriend. They have been dating for a little over a year and are clearly best friends as well as boyfriend and girlfriend. Our family likes the girlfriend very much. Recently, my son has come to my husband and I asking if he could go on vacation to Florida with his girlfriend. Her sister lives down there along with her husband. My husband and I know her family pretty well and believe we could trust them. It would just be he and the girl going on a plane themselves and staying down there with her sister for a few days for spring break. They both have jobs and would be paying for their own plane tickets. Is this okay? Would you let your son do this?