Sixth form age limit

So I’m a current year12 student and started a week at sixth form right now. Today my mum received a phone call from my teacher saying that I was too old to study sixth form because I’m 18 so I should move to college or somewhere else but I’ve enrolled and started my school year. Are they allow to kick me out because of my age. I was born on the 19th june 2005 so when a level finished I’m still 19 and I’m sure that sixth forms are for people between the age of 16-19. But I’m not sure if they have the right to exclude me from the school. Can someone answer me if they knew it thank you🙇*♂️🙇*♂️🙏🙏

IF the date listed on this post is correct, you are not 19 years old today.

Yeah I’ve just turned 18 this years june