This is Phoenix, he's 8 years old and skating the Ballard bowl with the big boys, and doing quite well thank you.
The one point I want to drive home is that without deep bowls to skate, these kids wouldn't ever have a chance to learn how to skate deep bowls. Kids aspire to do what the likes of Tony Hawk does, and this will never happen in a bowl that is shallow.
Also, another valid point is the comparison to other sports. Kids that are 13 years old, play on full sized courts and fields. So, there's no reason that skateparks should be small, just to accommodate the younger kids. They also need to skate full sized skateparks, just like Tony Hawk. The myth is that the whole park needs to be small for these kids, but these kids only stay beginners for about a year, after that they want something more challenging.
Phoenix is now 10 years old. And he's now progressing above the lip largely due to being able skate deeper bowls.