13 and 16 years old dating

Hi, my is son is a 13 year old but very mature, he gust got a girlfriend that he really likes, but she is 16 years old. They have a big age difference for teenagers, but they seem to be on the same wavelength as each other, and like each other a lot, so what should I do? Is it okay for him to date her, or is she to old for him?