|Oliva was one of many players with Cooperstown potential (Spokeo)|
Trosky's name isn't familiar to most baseball fans, but probably would be had he not retired prematurely due to migraines. The headaches effectively finished him at 28, by which point he already had half a Hall of Fame career in the books with 1,365 hits, 287 doubles, 216 home runs, 911 RBI, close to 30 bWAR, and a .313/.379/.551 batting line (135 OPS+). What's more, he'd already notched six seasons with at least 25 home runs and six with over 100 RBI (plus another with 93). Trosky, who retired for good in 1946, probably would have been a star for much of the 1940s given good health, as he would have been too old for military service (29 when Pearl Harbor was bombed).
Berger had a short career (11 years), and while he's remembered for establishing the rookie home run record of 38 in 1930 (which stood until 1987 and still remains the NL record shared with Frank Robinson), he was also a Cooperstown-caliber center fielder for the better part of the decade. He was selected to the first four All-Star Games starting in 1933, won two-thirds of the Triple Crown in 1935 with his league-leading 34 homers and 130 RBI, and totaled 35.8 bWAR through his first seven seasons. Berger remained productive into his early 30s, but injuries severely cut into his playing time and was all done by 35.
Through age 30, Junior was one of the best hitting shortstops of all-time. In addition to making seven All-Star teams and finishing in the top-10 of MVP voting six times, he'd won three RBI titles and driven in over 1,000 runs by that point. He'd also accumulated 41.4 bWAR, slugged 224 homers, and was nearing 1,600 hits. Stephens faded fast, failing to play 110 games in a year after turning 30.
Through his age 28 campaign, Pinson looked like a slam-dunk Hall of Famer. He had been exceptionally durable, having played no fewer than 154 games and getting at least 600 at-bats eight years in a row. His counting numbers were tremendous, including 1,746 hits, 918 runs, 313 doubles, 46.4 bWAR. A center fielder who blended power with speed, he only needed a few more solid seasons to round out his resume. Instead, he fell off the proverbial cliff, posting a sub-.700 OPS in seven of his final eight seasons and reaching a dozen big flies in a season only once.
Oliva got a late jump by not becoming a regular until he was 25, but made the most of his first eight full seasons. He was an All-Star every year, received MVP votes every year (four top-six finishes), and led the league in hits five times, doubles four times, and batting average three times. With his Hall of Fame peak complete, all he needed to do was tack on a handful of good-decent seasons to boost his counting numbers and make up for lost time at the beginning of his career, but he missed all but 10 games of the 1972 season and was never the same after that.
Besides having a fantastic name, Powell was also one of baseball's best power hitters in the 1960s and early '70s. Through 1972, his age-30 season, he'd already cranked 280 home runs and knocked in close to 1,000 runs. The 1970 AL MVP had also finished runner-up to Harmon Killebrew in 1969 and third to Brooks Robinson and Mickey Mantle in 1964. Powell would have one more good season (1975), but broke down rather quickly as he only once played more than 115 games in a season after turning 31.
Cedeno was another one who, at the dawn of the 1980s, appeared well on his way to Cooperstown. By the time he turned 30 in early 1981, he'd already totaled 1,576 hits, 475 stolen bases, and 49.2 bWAR while making four All-Star teams and winning five straight Gold Gloves from 1972 through 1976. A stolen base machine with solid power and on-base ability, he never again had more than 20 steals or 10 home runs in a season after turning 30.
Through 1979, Parker's age 28 season, he was already an MVP, World Series champion, two-time batting champ and three-time Gold Glove winner. He had batted at least .308 in each of his five full seasons and was a career .317/.370/.521 hitter (143 OPS+). He had the counting numbers to go along with those great rate stats, for he had already compiled more than 1,000 hits, 200 doubles, 100 homers, 500 runs/RBI, and close to 100 steals. With 32.3 bWAR under his belt (thanks to two seven-win seasons and a pair of six-win campaigns, all Parker needed was a couple more great seasons and a few more good ones to round out his resume, and he was a shoo-in.
If the Red Sox had held on to both of their Gold Dust Twins beyond 1980, we'd be talking about them (Jim Rice being the other) as two-thirds of Hall of Fame outfield. Because at the end of the '70s, Lynn (like Parker) looked liked he was going to sail into the Hall of Fame one day. He'd been dinged up by injuries and was merely okay in 1977, but was an All-Star every year and won four Gold Gloves. He'd also been league MVP in 1975, the same year he copped Rookie of the Year honors (becoming the first player to win both awards), and won the sabermetric Triple Crown in 1979. When Lynn headed out to California at age 29 he was a .308 hitter with 31.9 bWAR and almost 1,000 hits under his belt. He'd never win another Gold Glove, bat .300, or receive an MVP vote after that.
As the 1990s rolled around, it seemed a given that Donnie Baseball would have a plaque in Cooperstown someday. He'd been the American League's best two-way first baseman for much of the '80s, rivaling Wade Boggs as the best pure hitter in the game at that time. Coming off his age-28 season in 1989, Mattingly had made six straight All-Star teams and received five straight Gold Gloves. At that point in time he was also a career .323/.368/.521 hitter with 1,300 hits, including 272 doubles, and 33.2 bWAR under his belt. Unfortunately a bad back severely curtailed his production after that, limiting him to just 58 home runs and 9 bWAR over his final six seasons and causing him to retire before his 35th birthday.
One of the best all-around players of the 1980s, Straw should have been a lock for Cooperstown. By his 30th birthday he already had 280 home runs, 201 stolen bases, 40.1 bWAR, and a career 144 OPS+. He'd also made eight straight All-Star teams, won the 1983 NL Rookie of the Year award, and finished in the top-10 of MVP voting four times. Sadly, injuries and substance abuse problems ruined the second half of his career, limiting him to just 335 games over his final eight seasons.
Pre-2004 Nomar was on track to be one of the greatest shortstops who ever lived (Ted Williams thought so). He'd batted over .300 with at least 21 home runs, 100 runs, 98 RBI, and 190 hits in each of his six full seasons, finishing in the top-11 in the MVP voting in all of them and compiling 41.2 bWAR up to that point. A career .323/.370/.555 hitter up to that point, all he had to do was stay healthy. Easier said than done. Only twice more did Garciaparra play more than half a season, and he retired a shell of his former self following a string of disappointing seasons (save 2006) after leaving Boston midway through their historic 2004 journey.
Here's a guy who really fell off the face of the earth in his 30s. Through age 30 he looked like a lock for Cooperstown, as he already had 368 home runs, 1,117 RBI, and 61 bWAR by that point, not to mention 10 straight Gold Gloves. If Jones falls short of the Hall, it will be because he became a spare part with 1.8 bWAR over his final five seasons.