Stephen Strasburg plopped into a chair and faced his locker, one of the double-wide stalls reserved for veterans in the Washington Nationals’ clubhouse, the kind he would have preferred to let someone else have. He glanced at his hand and counted his fingers as he extended them, simple math he needed to prove how long it had been: 2010, 2011, 2012. . . . His eyes widened, and he nodded. It was hard to believe, but it was true: Strasburg had just started his fifth spring training.

“That is kind of strange,” pitching coach Steve McCatty said. “It’s weird.”

“Time flies,” Strasburg said, a sentiment his friends in the room understood well. During their ascension from doormat to contender, the Nationals have been driven and defined by a youthful, dominant pitching staff. The staff remains excellent, but it is not quite so young anymore. Strasburg, Jordan Zimmermann, Gio Gonzalez, Drew Storen, Tyler Clippard, Ross Detwiler, Craig Stammen — they have all left their early 20s behind.

They have attended each other’s weddings. Two of them, Strasburg and Zimmermann, became fathers this winter. They have celebrated each other’s awards and raises. They have supported each other through failures and demotions. As they have helped transform the Nationals, they have grown up together.

“I told Clip, ‘I still can’t wrap my head around Stras talking about his kid,’ ” Storen said. “That’s unbelievable to me. It’s cool. You’re able to see people grow up, and at the same time you realize how much you’ve grown up yourself.”

The Nationals’ familiar pitchers have treaded carefully into a sort of baseball adolescence. They can no longer consider themselves rookies or inexperienced, but they are not ready to call themselves old hands, either. Gonzalez, Clippard and Detwiler may be closer to 30 than 25, but they haven’t gotten there yet.

“I wouldn’t say we’re veterans,” Zimmermann said. “But we’ve been up here for a few years and kind of know what goes on. It’s definitely nice coming to spring training. You feel a lot more comfortable, not like the new guy sitting in the corner, you know?”

Last year, Strasburg arrived early for spring training and found an extra-large locker awaiting him. No one had moved into the smaller one next to it, so he told clubhouse manager Mike Wallace to give his to Dan Haren. This year, Strasburg wanted to give his wide locker to Doug Fister, but he arrived too late — Fister’s stuff was already moved in.

“I want the younger guys to be approachable, and if they have any questions, I’ll try to help them the best I can,” Strasburg said. “But at the same time, I don’t feel like I have all the answers, either.”

“I remember the first couple years, I was like, ‘Man, I wonder what it’s like to have five or six spring trainings under your belt. You must feel like such a veteran,’ ” Stammen said. “It doesn’t feel that way. I still feel like I’m trying to earn my way. But it’s nice to have made it this far with one team.”

The Nationals derive benefits from their pitching staff’s years together. If Gonzalez drops his arm even a smidge during his delivery, Zimmermann can tell immediately. They know when to give one another space, but they also know how to offer criticism without offending.

“They watch each other,” McCatty said. “I always thought it was the guys that you pitch with for a period of time, that when you talk to them, they know themselves pretty well but they know you, too. You can exchange things.”

They know how to tease each other, too. In the rare moments Gonzalez remains silent, Zimmermann might walk past him and say, “One of those days, huh?” On Saturday, Strasburg said he looked forward to learning from Fister, whose locker was to the left of his. On the right was Gonzalez.

“If I can get a couple words in with him over Gio’s chatter, then that will be good,” Strasburg said, laughing.

On Saturday morning, Clippard was the last pitcher to reach the practice field. (“We were a little ahead of schedule,” Manager Matt Williams said, “and Clip was really the only one that was on time today.”) As Clippard jogged to join his teammates, they rose and gave him a standing ovation.

As they have gained experience, they have also grown more expensive for the Nationals. In 2012, Strasburg, Zimmermann, Gonzalez, Storen and Clippard combined to make $10.7 million. This year, after all received raises through arbitration, they will earn a total of $29.3 million. Next year, Zimmermann will make $16.5 million.

Time moves so fast that they barely realized how time has passed — “it’s crazy,” Stammen said. But Saturday, the first workout of spring, provided a benchmark. Strasburg thought back to his first trip to Viera, in the fall of 2009 after the Nationals drafted him.

“When I first got here after I signed, I get to the airport in Orlando,” Strasburg said. “I go get my rental car. I’m driving out in the darkness. I’m like, ‘Where am I going?’ I can’t see anything. It took forever. I’m like, ‘Where is this place?’ Now I have a little better idea of how things work.”

This winter, Strasburg’s wife and Zimmermann’s FaceTimed constantly, swapping stories about their newborns. “I’ve been up here for four years now,” Zimmermann said. “I got a kid. Married. Who knows what’s going to come next?”