In Sweden our age grids are Youth: 11-13 (you're not allowed to compete with score sheets under the age of 11, no exceptions), Junior: 12-16, Senior: 15+. So if you're 12 or 13 you can be either youth or junior, and 15 or 16 either a junior or senior. However you are allowed to have under age athletes on an older team in level 1 through 5 (level 6 national champions becomes the national team so they have different rules), as long as 80% of the athletes are the correct age for the division. It keeps the divisions fairly strict on age, but gives smaller "gyms" the option of fielding a senior/junior team with a few younger athletes. You're also allowed up to 2 seniors/juniors on a younger team if your "gym" doesn't have a team in their age range.