That there should be an automatic conversion between NI category M (for the under 21's) to category A once an employee turns 21

In a busy workplace, this is easily missed, causing employers to run up debts to HMRC. I have less than 20 employees and I still missed oneI I see that another client has a similar concern when pension age is reached so please action these asap. Thanks

PS, I have only guessed at the category!