I found the perfect angle for my kicking, and a slow PC allowed me to stop enough opposing kicks to beat level 5. But it appears that you can't get your kicks past the keeper at level 6, because all the high scores end at 50, which would be perfect through 5 levels but failing to score at level 6.
This is a very fun game. It reminds me of something I might find on CandyStand.com The music is also jammin.