My daughter, MJ did tops training last year, even though she was too young to test (6). She loved it, but again, she was 6. She was also training it in addition to her developmental group. This year, she's on L4 team and also training Tops. Not all the girls who train for Tops at our gym will actually test, but the workout is outstanding and great for strength and flexibility. There are a LOT of parents that push their kids to come, though. I heard one girl going into tops one day, and somebody told her to have fun and she said, "I'm not here to have fun I'm here to work" lol.
My daughter didn't start gym until she was 6, and she didn't mind the added tops workouts...and our gym doesn't do them every week. I don't think at 5 I would have put her in them, though. Too much of a risk for burn out. And if she hadn't liked them, we would have stopped going-again, at that age, it's very easy for them to burn out if they go too much and it just isn't fun anymore.