The simple answer is: no. Students can start at any level, but if they are new to the program, a safe place to start is Level 4 or lower, especially if they are children. Here are some tips (based on my experience with RCM) to help you figure out where to start a student.
Overview
There are three main tiers:
Elementary: Prep-Level 4
Great place to start for any age. These are developmental levels that emphasize student performance over technique and tone quality. Students develop important foundations such as diction, vowel formation, intonation, rhythm, phrasing and the focus is on developing expressive performances.
Intermediate: Level 5-Level 8
At the Intermediate Level, students must take a Theory co-requisite, perform 4 or more songs and study a vocalize. The Technical Requirements become more complex. Students are required to perform one foreign language selection and are evaluated on tone quality in addition to basics from the Elementary Level.
Advanced: Levels 9-10 and ARCT
This is a more collegiate level of singing with co-requisites. The repertoire is much more sophisticated and requires advanced technique. Students perform a recitative as part of the exam.
Age of the student
The RCM Voice Syllabus is not designed to be age specific, but if you are teaching a young singer, consider the longer path ahead. The preparatory level is a great place to start for grades 2-4 (ages 10 and under). Consider Level 1 at grade 4, if they are more secure with musicianship skills, but Level 1 or 2 might also be appropriate for a student in Junior High. I prepared a third grade singer for Level 1. She is now in 6th grade and is doing Level 4. I may slow her down and stay in Levels 5 for the middle school years to allow her voice to mature, since in her specific case, the voice is very young.
I started a 6th grader in Level 1 since it was her first exam to give her a chance to develop musicianship skills. We skipped Level 2 and she is currently doing Level 3 as a 7th grader which is appropriate level for her vocally. Level 4 will be appropriate for 8th grade and she can decide if she will continue into the intermediate Level (5-8) in high school.
I currently have an 8th grader in Level 5 and this is an excellent place for her since she is an experienced musician and has strong keyboard skills.
The youngest Level 6 I have prepared is currently a high school freshman with a very mature voice. If she continues to take one exam per year, she could take Level 8 her Junior Year and Level 9 her senior year. Level 9 would be very challenging, and we may decide to spend two years preparing Level 8.
Musicianship
You may find that an older student benefits from starting at a level where they can handle the musicianship skills, even if their vocal abilities may be at a higher level. If you believe they may take future exams, start off at a lower level, establish the musicianships skills and advance as needed. In the end, you want your student to be successful and the musicianship skills can be challenging for some singers.
Adults
Level 3 is a great place to consider starting an adult singer who has some musical experience. You may find the repertoire in Levels 1-2 too juvenile for an adult, but if their musicianship skills are very weak, start lower and build. Consider starting with the technical exercises and ear training for level 1 with your adult student and observing how long it takes them to master some fo the skills for Level 1. This will help you determine where to start them. It is better to establish good foundations than jump to Levels with more sophisticated repertoire right away. You can also skip a Level and advance as needed.