CARSON, Calif. -- He's so exuberant his teammates sometimes tell him to tone it down. Then again, it's hard to blame Freddy Adu.

He is, after all, 15.

"He's definitely that age," D.C. United midfielder Ben Olsen said, shaking his head and chuckling. "He's a great kid, fun-loving. He likes to hang out with all the guys. Sometimes we have to tell him to shut up. It's like having your kid brother in the locker room."

Adu was a wide-eyed, 14-year-old fan at last year's MLS Cup. He returns to Major League Soccer's championship game wearing the uniform of D.C. United, who play the Kansas City Wizards for the title Sunday.

It's all great fun for Adu.

"I'm energetic and have a lot of energy to share, and sometimes they do have to tell me to shut up because I talk so much," Adu said. "We make fun of each other back and forth."

Some of his teammates are more than twice his age, and Adu doesn't mind being regarded as the team's younger brother.

"It's so good to know that these guys support you and have accepted you into the team," he said. "It just makes it easier for me out there. I feel very comfortable."

Adu, poised and articulate, already has completed high school. He signed a $500,000 deal in November 2003 to become the league's highest-paid player. He also has a $1 million endorsement deal with Nike.

Not that he needs it.

"If I need money, I get it from my mom," Adu said. "She makes sure I'm not out of control, so that's good."

Adu, 5-foot-8 and 140 pounds, appeared in all of United's 30 games, starting 14. He had five goals and three assists.

"At first, it wasn't easy at all," Adu said. "It was definitely a learning experience. I didn't think it was going to be easy in the first place, but it was certainly harder than I thought. With the help of my teammates, my coaches, and, most importantly, my family, I was able to make it through it."

The first half of the season was particularly difficult.

"The second half of the season, I played much, much better. I scored three goals and had three assists in the second half and I was very happy with that because I didn't play too well in the first half," he said. "I knew I could play better. I grew up a lot. My teammates told me, 'Just go out there and play. You're a soccer player."'

United teammate Ryan Nelsen calls Adu "incredible."

"He's twice the player he was when he first turned out," Nelsen said. "Once he becomes better off the ball, he can become a complete package."

As an international celebrity, Adu also had to deal with constant off-the-field demands.

"It must have been so hard with everybody wanting a piece of him," Nelsen said. "I told him, 'You've got to keep your feet on the ground because when all is said and done, what you're doing on the field is what's important.' It's amazing what he's done."

United coach Peter Nowak lauded Adu for his "work ethic and professionalism." Adu said he has had to work on moving without the ball, and on reading the game and thinking a play ahead.

Then there's the fact that he's competing against full-grown men who are trying to knock him off the ball, tackle or intimidate him.

"All I've got to do is use my quickness to get away from them," Adu said. "In the beginning, I didn't really recognize that, but from talking to Peter, it's 'Hey, don't worry about that stuff.' It's what's in here, not in the body," he said, tapping his head. "Just use it to your advantage."

Adu was particularly pleased with one of his goals -- the game-winner in a 1-0 victory over the MetroStars on Oct. 2.

"New York and D.C. are great rivals," he said. "And being able to get that goal to help out the team, it was awesome."

Another big moment awaits June 2. He turns 16.

"I can't wait to drive myself wherever I want to go, instead of always having to get rides," he said.