RANCHO CUCAMONGA – Juan Castro is feeling something unusual as he articulates a thought.

The longtime big-league backup infielder, now a roving instructor across the Dodgers minor-league system, has been asked about the organization’s top pitching prospect, a young Mexican left-hander named Julio Urias, and the natural comparisons between him and former Dodgers sensation Fernando Valenzuela.

Before answering, Castro pauses and exhales.

“I’m getting goosebumps,” he says. “You know he’s a Dodger. You know he’s a lefty. You know he’s from Mexico. And I bet you a lot of the Mexican people are waiting for another Fernando.”

Valenzuela, a tender 19 when he debuted in the majors, and Urias, 18, are from towns four hours apart in northwest Mexico. Castro hails from a city halfway between, and he remembers being riveted by every one of Valenzuela’s starts in the summer of 1980, when he was 16 and he and his dad would carry chairs to the house of the only neighbor who had cable.

“Fernandomania’s not gonna happen ever again,” Castro said. “But people want to see somebody similar, and I think this kid can be someone special like that.”

Urias is already special, in a historical sense. Few 16-year-olds pitch in a full season of professional ball, but he did that for three months last year with the Low-A Great Lakes Loons.

He followed that up with another starring season at High-A Rancho Cucamonga this year. Urias posted a 2.36 ERA in 872/3 innings against hitters who were, on average, five years older, striking out 109 while issuing 37 walks. He hit more batters (7) than he allowed home runs (4). He became the youngest player to participate in the All-Star Futures Game and recorded a strikeout in a scoreless inning.

But Urias’ season is done. Despite the possibility he is already good enough to retire major-league hitters in short stints, he will not be called up to the Dodgers this September, because doing so would accelerate his free-agency clock; because some evidence supports the idea his teenage arm can handle only so many innings at this stage; because promoting him now would be considered downright radical; and because the benefits of 10 or so good innings would be minimal compared to all that.

Teenagers don’t often pitch in the majors. It’s been nine years since anybody has before turning 20, and that was Felix Hernandez, another special case.

No 18-year-old has pitched in the majors since Jose Rijo with the Yankees some 30 years ago. It’s conceivable to think Urias could make his major-league debut before he turns 19 next Aug. 12; it’s almost inconceivable to think, at the rate he’s been progressing, that he won’t debut before he turns 20 in August 2016.

SO, WHY NOT NOW?

DeJon Watson laughs at the question, even when prefaced by all the aforementioned qualifiers.

The Dodgers’ vice president of player development has heard it a lot this season: Would Urias be able to handle the majors at this age?

“All I can say is that this young man is developing at a rapid pace,” Watson said. “All the speculations that are out there, that goes with all the hype. You have to be able to keep him grounded.”

Matt Herges doesn’t laugh. The former Dodgers reliever, who served as Urias’ pitching coach in Rancho Cucamonga this season, intimates a desire to move him up has existed for a while.

“It’s hard to not rush him along, but our No. 1 priority as caretakers of this kid, this special talent that we have, is to do right by him,” Herges said. “You never really know when you’re gonna blow, if you’re gonna blow. The Nationals handled Stephen Strasburg with kid gloves, did everything by the book, and it still didn’t work. But we gotta be smart with Julio. But then again, we still want him to develop into who we think he can be.”

Forget what he can be — what is he now?

Urias is the son of a former Mexican League catcher the Dodgers signed after spotting him on the same scouting trip that netted them Yasiel Puig.

From an easy, repeatable delivery, Urias now throws a fastball, a changeup, a curveball and a slider. In describing them, some combine the latter two into one all-encompassing breaking ball. His fastball regularly sits at 93 or 94 mph, reaching 97 on rare occasions.

“It’s not just that the quality of each pitch is that good,” Herges said. “It is, but what makes it most impressive he can command all three of them, and that’s unheard of.”

Urias said last week he is 6-foot-2 and 215 pounds. That might be a stretch, but he’s assuredly closer to that than his listed 5-11 and 160 pounds. Since he signed, his weakness from a scouting perspective has been that body; in no uncertain terms, many have wondered if he’ll get fat as he ages.

It started to happen toward the end of 2013, but he showed up at spring training looking fit, if not trim.

“Last year he got really heavy,” Watson said. “That was one of the things we worked on over the winter.”

Because of Urias’ precociousness, the Dodgers are essentially forced to treat him differently than other minor leaguers. Herges reminds his catchers to give Urias more leeway when shaking himoff.

“Have I seen something mechanically that I could even touch?” Herges asks. “No. A lot of these kids, I’ll talk about an approach, like OK, why was this sequence of pitches not good enough? And it’s like it’s the first time they’ve ever thought of it. With Julio, it’s like he’s been brought up in a baseball bubble where anything you could talk about already makes sense to him.”

And he turned 18 three weeks ago.

“When I was 18, I was just trying to have someone sign me, to come to America and to play pro ball,” said Urias’ teammate, roommate and often his translator, 24-year-old Venezuelan right-hander Luis Meza. “He’s 18, and he’s spectacular.”

ABOUT APRIL

Herges has a rule: When his pitchers are removed from a game mid-inning, they must remain in the dugout until that half of the inning is over.

On April 25, Urias did not follow the rule. When he was pulled after issuing four walks and getting two outs, he headed straight to the clubhouse.

“He kinda melted down,” Herges said. “So I went in there, immediately, and I was furious. This was the first inning that I’d ever seen him struggle. And he was sitting in his chair, and he was broken.

“I said to myself, ‘Wow, I get now the expectations that he feels. The magnitude of him not coming through out there, to him, is more than any other kid we have. And that woke me up to it, and I let him be.”

They smoothed things over the following day, and Urias did not get pulled mid-inning because of ineffectiveness the rest of the season.

But Urias did not start that April 25 game. Clayton Kershaw did, in his first rehab appearance while working his way back to the majors, and Urias followed.

“‘Here’s my coming out party,’” Watson imagines him thinking. “‘Here’s Kershaw, and I’m coming out right behind him.’”

Said Watson: “That was his biggest struggle.”

Now, Urias talks about April as a “tough moment,” one that taught him how to change the rhythm of hitters, how to dictate his own pace in the hitters’ paradise that is the California League.

“To me, this year was about mental growth for him,” Watson said. “Once we got him exposed to the Midwest League (in 2013), the media was going to come after this cat. How was he going to manage the expectations, the hype?”

Watson stops.

“I didn’t realize the hype machine was going to go this fast,” he said.

NEXT UP

After Urias appeared as a surprise starter in a big-league spring-training game in March and confidently pitched a 1-2-3 inning against the San Diego Padres, he spoke to the media en masse for the first time — just as confidently.

“My goal is to finish this season in the major leagues,” he said then. “If I can’t, then Double-A.”

We don’t know if the Dodgers ever seriously considered promoting him to Double-A Chattanooga this season. Even if they did, he wouldn’t have had many innings left in his arm to do much there. The Dodgers wanted to keep him to fewer than 90. They’ll probably limit him to 120 in 2015, and, if the pattern continues, 150 in 2016.

That, as much as anything, is the biggest impediment to Urias’ big-league arrival. But if he continues to pitch like he did in July and August, impediments have a way of going away.

Urias posted a 0.74 ERA in 361/3 innings over his final nine outings this year.

“I’ve impressed myself,” Urias said through a translator. “It’s been a great year for me, a lot of things going on. There were things that I didn’t expect to happen.”

Among those things: his April struggles, the Futures Game appearance, the downright dominance, maybe even the lack of a call-up, although he wouldn’t say it.

“At the beginning, that was my goal,” he said. “But it’s not in my control. It’s in the Dodgers’ control, and I know the Dodgers are doing the best for me. If I can’t make it this year, that’s my goal for my next year.”

Yeah, next year makes a lot of sense.

Contact the writer: pmoura@ocregister.com