You need to get an ACU novice licence to get started.
You will need a bike and all the gear. We would suggest starting on a Supertwin as they are cheap and easy to ride.
See link below:-
https://www.acu.org.uk/acu-events/competitor-training-course.aspx
You will need to be accompanied by a parent or guardian if you are under 18. You can start at 14 years old.
You can then start racing at club level and progress from there.
It is very expensive the further you progress, although you can start racing for a season for around £10,000 or less with a cheap bike like a Supertwin. This increases a lot as you progress, with a season in Nationals probably costing over £50,000 for a competitive bike.
If you are very successful you might be able to attract sponsorship to help with costs.
The chances of international success are very very slim, but racing is an incredible feeling, particularly when you win.
It will be painful at times as you will fall and be injured, hopefully not seriously, and there is a small risk of death.
Good luck and take care.
British Superbike School 