My DD (9 tomorrow) competed as a level 4 last year and is training for Level 5 - she will start competing as a level 5 in a few months. When she was 3 or 4 and taking regular recreational gymnastics classes, the gym saw potential and asked if we would put her in the "Hot Shots" class that met for 1 1/2 hours (instead of 1), twice a week. We agreed to the 1 1/2 hours, but only once a week because it conflicted with something else. By about age 6 she was on the "training team", going two hours at a time, twice a week. As a level 4 last year she was going 3 days a week, 2 hours at a time. At the end of last season they were bumped up to 3 hours at a time, them up to 4 days a week, which is where she is now. (12 hours a week; she finally had to drop soccer.)
They compete at Level 4 up to Level 10, then Elite (the gymnasts you see on TV are Elites). If you or your DD really have "ambition" she needs to be a Level 4 by about 7 years old, in order to progess to Elite by age 14 or so. (Of course, if she has extraordinary talent, she could progess faster.) But with that said, there are Level 4s who are 6 and level 4s who are 11. DD is in third grade and there are a couple of girls in her Level 5 group who are in 7th grade. Some girls spend 6 months at one level; others spend 2 years at that level.