For this achievement you have to do exactly what it says... Max your stats out, all of them.
Here's what you need for each stat to max:
Air: 14,000 Seconds (Around 4-5 Hours)
Manual: 140,000 Feet
Grind: 140,000 Feet
Spin: 1000 Rot.
Wallride: 10,000 Feet
Special: 512 Special Tricks Done
Air Happens whenever, you're player is airborn... Duh! A Manual is when your character is on two of his wheels balancing on the board, and happens when you press Up and Down one after the other. You grind with Y. Invert is when your player is balancing on the edge of a quarterpipe. Its done by appraoching a quaterpipe perpedicularily, and pressing Y. Spin, are simply rotations. Wallrides are when you jump into a wall, and press Y. And A special, is a trick that can only be preformed when your special meter is full. The trick will appear in a Differetn Colour on the bottom when it is preformed.
You Can access your stats at anytime, by pausing the game and going into Skater Options and then Stats.