25) Rex Brothers’ 2013 season (Age 23 season)
Rex Brothers makes this list as the only reliever on here and it’s because they don’t pitch enough innings but Brothers pitched a lot for the Rockies in 2013 and he was phenomenal.
Brothers took over in the closer role mid-season after Rafael Betancourt suffered through appendicitis and multiple other injuries. In 72 games in 2013, he finished 40 games and he had 19 saves in 21 opportunities along with 12 holds. Overall, he had an ERA of 1.72 with a FIP of 3.36 and an ERA+ of 257. He allowed less than seven hits per nine innings, walked 4.8 per nine innings, and struck out more than 10 per nine innings. He had a WAR of 3.1.
The injury bug ended up hitting Brothers the next season and in ensuing seasons as 2013 was his last full season in the majors. He returned to the majors with the Cubs in 2020 and he is still in their organization.
24) Jeff Francis’ 2006 season (Age 25 season)
Jeff Francis’ 2006 season was not as good as his 2007 but he was 26 in 2007 and therefore, that season does not qualify. However, his 2006 season still qualifies for our list.
In 2006, the Rockies, despite only having only a 76-86 record, had their best record since 2000 and Francis was part of the reason behind that. In his second full MLB season, he went 13-11 with a 4.16 ERA in 32 starts (199 innings). In those 199 innings, he averaged 8.5 hits, 0.8 home runs, 3.1 walks, and 5.3 strikeouts per nine innings. That home run average was 9th-best among NL qualifiers. He also had a WAR of 3.3.