drama school at 16 or 18Watch
For straight Acting you need to go to an accredited drama school (one that has a graduate showcase and is eligible for Spotlight entry) aged 18. Sometimes even 18 is too young for actors.
For musical theatre you have the choice to do a L6 diploma at 16 or a degree or diploma at 18. Depends on whether you are ready for professional training and what local opportunities there are. My own daughter chose to go away to train at age 16 at a funded school where she could do A Levels AND a dance/MT Diploma as her dance was already at a high standard.
There are several ways to get to drama school. Some young people take A levels alongside local dance/singing training and youth theatre/drama groups. Others do a Btec in performing arts which can, if offered by a good college who auditions and has high standards be excellent preparation. However there are lots of local colleges offering pretty average Btec filled with those who have chosen it cause drama is easy, it’s just messing about! So if that’s all that’s on offer locally a young person might apply for a post 16 course further from home. Some are free eg LIPA, some are fee paying eg Arts Ed.