no idea how he stayed in the major leagues more than a couple of years. He was ATROCIOUS in his 20s
https://www.baseball-reference.com/players/m/mahompa01.shtml
ERAs by age
21 - 5.04
22 - 7.71
23 - 4.73
24 - 6.37
25 - 6.91
26 - 8.10
Then out of the league for a year, and came back at age 28 to average like a 5.00 ERA from then on