Compulsory meets are L1-5 and all kids do the same routines. USAG requires qualifying scores for mobility starting at L4.
Once you 'score out' at a USAG sanctioned meet, you may move up if your gym allows it. Some gyms are more picky than others.....at our gym, the coach requires at least a 35 all around to move, even though USAG requires a 32. Some gyms require a whole season, (or more) at a level, some gyms just want one meet to move up....depends. Ours is big on competing the whole season, and getting the gymnasts to look as perfect as possible for the state meet, then on to the next level.
L6-10 are optional levels, and the routines are put together by the coaches and athletes. They must have a minimum # of skills and requirements and can be tailor made to the athletes strengths. My DD can't wait for level 6, she is already listening to floor music, and inventing dance moves....very cute.
Many states have their compulsory season in September-December, and then optional season starts January-April. There are meets in the jan-April time frame for the lower levels too and some gyms use those spring meets as mobility meets, as ours does. We do the state meet, and then after that all the girls try for their new skills to try and make the next level in February or March....