Perhaps it is the polished way he carries himself, or the fact he is in his fourth full season.
Whatever the case, Zimmerman is comfortable in his own skin, and he is thrilled at his newfound All-Star status.
"Everyone thinks I'm like 30 years old," Zimmerman said. "The first couple of years, I feel like that [leadership] was kind of pushed upon me, and I wasn't ready for it. It's hard to come into a big league clubhouse and be a 21- or 22-year-old kid and be looked upon to be a leader, because it takes a lot of respect to get in front of those guys and say things."
Now he is starting to feel like a leader, albeit a quiet one.
"For me, the first couple of years, I was very quiet," Zimmerman said. "I still am very quiet. You have to make sure you have the respect of your teammates and your peers first, but now I feel like I'm past that and I'm an old 24, if you could say that. Now, I think I enjoy that role."
Zimmerman is the first homegrown player from the Nationals to go to the All-Star Game, and it's a big deal. After all, he is the face of the franchise and is expected to be in Washington for the next five years.
At the break, Zimmerman is hitting .288 with 13 home runs and 52 RBIs. The highlight of the first half came early in the season, when he posted a 30-game hitting streak, the longest in baseball this season.
The accomplishment earned Zimmerman a lot of national recognition. No longer is he overshadowed by his childhood friend, Mets third baseman David Wright, or baseball hero, Braves third sacker Chipper Jones. In fact, Zimmerman was voted into the All-Star Game as a reserve by his peers.
"The fans mean everything to this game, but to get voted in from the people you play against day in and day out, you want them to have that utmost respect for you," Zimmerman said. "I'm going to try to do everything I can. You might not get to do it again. It's a huge honor. I'm going to get my family to come out there. You never know what's going to happen. I'm going to take advantage of it, enjoy myself and have fun."
Being at his first All-Star Game is even more special because his mother, Cheryl, will be in attendance. Cheryl has been afflicted with multiple sclerosis, an unpredictable disease that affects the central nervous system, since 1995.
During the first five years of her illness, Cheryl was able to work as a teacher, but it grew worse by 2000. She is now confined to a wheelchair.
Ryan said Cheryl's illness helped him become even keel throughout his life. It explains why one never sees him get angry with the media or with umpires in public.
"That's a big part of it." Ryan said. "Me and my brother [Shawn] had to do some things that younger kids wouldn't have to do. We were not the only kids that ever had to deal with something like that. That added to my [composure]. I don't get too high or too low.
"Before that, that's the way we were brought up. That's the way my parents were when we were young. I just think it rubbed off on us."
Cheryl continues to hang in there. Today she is one of the Board of Directors of ziMS Foundation, which raises money to help find a cure for ALS. Ryan is the president of the foundation.
Asked how Cheryl is doing these days, Ryan said, "It's nothing really. It's just kind of steady. There is no cure, there is nothing, so it's the same thing every day. Obviously, we have dealt with it for a long time. It's almost second nature to us.
"It's good to get her and my family out to St. Louis to see this. It will be a lot of fun for her."
Besides having his mother around, Zimmerman also wants to learn about the history of baseball. That's why is looking forward to mingling with retired players who participated in previous All-Star Games.
"I want to see some of the old-timer guys," he said. "With Interleague [Play], you get to meet most of the guys in the American League. I think seeing some of the guys that shaped the game is going to be more exciting."