I believe it is:
under 9 months (novice, not twisting knee locks)
9-18 months (beginner, no twisting knee locks)
18-36 months (intermediate, no twisting knee locks)
36 months and above (advanced/ heel hooks allowed)
Professional divisions.
Use your judgement- not a lot of people follow these guidelines- there are lots of career "intermediate" grapplers and ex collegiate wrestlers who are competing in there as well.