Olympus Planet Fitness has pathetic client service

I'm a single mum of 2 teenagers aged 16 and 17. Last week my kids signed up for the free 2 week trial as they would like to start going to the gym daily. They went twice last week and loved it. I was going to take a membership for all 3 of us. Today my son got to the gym and they did not allow him in which is frustrating as we live in Faerie Glen opposite the Virgin Active but my kids wanted to go to Planet Fitness. We had to go back and fetch him. I called your sales manager Nathan now, and he said that my son is 16 that is why they turned him away tonight yet he was allowed twice last week which doesn't make sense. I'm actually so put off that I would not take a membership with you guys as this is so unprofessional. He was not helpful at all and could answer as if this is your policy, why did you initially allow him at the gym?