You can’t become an approved driving instructor (ADI) until you've had a full licence for 3 years or more.
You have to have had your full licence for at least 3 years to supervise a learner driver.
You can usually apply to start the qualifying process 6 months before the 3rd anniversary of getting your full licence. This is because it will take at least 6 months to qualify as an ADI.
It’s against the law for you to charge a fee to teach someone to drive if you’re not an ADI.