MLB.com's Prospect Watch, only includes players with rookie status in 2013.
The top 50 also includes two of the four prospects traded by the Royals to the Rays for pitchers James Shields and Wade Davis. Outfielder Wil Myers is ranked No. 4 and pitcher Jake Odorizzi is No. 45.
The top three in the nation are, in order, Rangers shortstop Jurickson Profar, O's pitcher Dylan Bundy and Cardinals outfielder Oscar Taveras.
In terms of team rankings, based on the reverse order of players in the Top 100, Kansas City ranks 14th among the 30 organizations with 184 points. The Mariners are first with five prospects and 351 points and the Cardinals second with six prospects and 340 points.
Starling, 20, was a popular first-round choice in the 2011 First-Year Draft because he's from the Kansas City area in Gardner. He decided to sign with the Royals instead of playing quarterback at the University of Nebraska.
His first season was 2012, and the right-handed batter had a .275 average, 10 home runs and 33 RBIs in 53 games for Rookie-level Burlington.
"We realized pretty quickly that he was far more advanced defensively than we expected," said J.J. Picollo, assistant general manager/scouting and player development. "We knew he could run, we knew he could throw but his instincts were further along than we anticipated and he continued to get better. A lot of the little nuances -- cutting balls off, throwing to the right base; he picked up on things really quickly. He has become a premium center fielder and a guy we think can stay in center field."
At the plate, Starling struck out in 70 of his 200 at-bats; he walked 28 times and had a .371 on-base percentage. Picollo said Starling worked on cutting back on his strikeouts and improved his situational hitting during the season.
"He made great progress. There are still some things we are working on in his swing, like a lot of young hitters, but his production was real good. He hit in the middle of the lineup on a pretty good team and was a great run producer for them," Picollo said.
Starling will probably start this season at Class A Lexington.
Zimmer, 21, is a former third baseman who switched to pitching at the University of San Francisco and was the Royals' first-round Draft choice in 2012.
In his first pro season, Zimmer had a combined record of 3-3 and a 2.04 ERA in nine starts for Rookie-level Surprise and Class A Kane County. In 39 2/3 innings, he had 42 strikeouts and just eight walks.
After the season, bone chips –- a condition known to the Royals when they drafted him -- were removed from Zimmer's right elbow. He's recovering on pace and has no restrictions on his throwing.
"There's no reason to think he's going to be slowed up at all," Picollo said.
Zimmer will move up to Class A Wilmington this year.
"Our feeling was when we drafted him that he would be a fast mover, and the thing we have to keep in mind is that he's only pitched for two years, so you look for the little things in a pitcher -- holding runners, fielding his position," Picollo said. "How has he adapted with that? Because it's going to come into play when he gets to Double-A and it's going to be more challenging at Triple-A and in the big leagues. We want him to be a complete pitcher, but his stuff is certainly far advanced for a guy in his first year so we do expect him to move quickly."
Zimmer, in addition to a fastball, has an above-average curveball and slider and he's worked well with a changeup.
Ventura, 21, is a right-hander who started the All-Star Futures Game for the World team -- Odorizzi started for the U.S. squad -- and has been invited to the Royals' Major League Spring Training camp this year. He was a skinny kid when he signed in 2009.
"We just saw him in the winter camp at Arizona," Picollo said. "His body is growing and, with age, he's adding some weight. His body is catching up and he looks a lot more mature physically, and with an arm that fast, you've got to be careful with him because his natural strength and his man strength are not quite there yet."
Not that Ventura needed the extra weight to hit 100 mph on the radar gun. But he's accomplished other things.
"The most impressive thing he did last year was he really started to control his delivery better. He wasn't trying physically to hump up and throw balls by hitters; he really just trusted his delivery and his command got better and his breaking ball got better," Picollo said.
"As a young pitcher, he just tried to throw 100 and not worry about his mechanics and now he realizes, 'I can throw 98 to 100 staying within my delivery.' I think that will help long term with his health and being a more complete pitcher."
Dick Kaegel is a reporter for MLB.com.