The 1969 Mets had two young pitchers destined to win more than 300 games apiece — Tom Seaver (311 wins) and Nolan Ryan (324). The staff also included Jerry Koosman (222 wins) and Tug McGraw (96 wins and 180 saves), who weren't Cooperstown-bound but destined for long and distinguished careers.
In 1969 Seaver was 24, and he pitched 271 innings. Koosman was 26 and threw 241 innings. McGraw was 24 and pitched more than 100 innings, mostly in relief. Ryan was 22 and had a much lighter workload (15 relief outings, 10 starts, 89-plus innings), but he had missed almost all of the 1967 season with arm problems and was notoriously wild.
By today's standards, Seaver, Koosman and McGraw had heavy workloads for pitchers so young. Yet they weren't burned out by such use.
Of course, the Mets also had Gary Gentry, 22, regarded as every bit a match in talent to the others. He made 35 starts, pitched 233-plus innings and was fried before he reached 30.
We don't have pitch counts for these guys, but we do know how many batters they faced per game. This counts in longevity; in his book "The Diamond Appraised," Craig Wright used batters-faced to study pitcher durability and concluded that, especially for pitchers under age 25, BFP should be limited to an average of 30 per start (or less).
Koosman was a tad under 30 in 1969. Seaver was at 31. Gentry was at 27. Ryan, in his 10 starts, was at 24. Wright thinks Seaver, as great as he was, might have had an even greater career had he been handled a bit more carefully in his first few years with the Mets.
Most organizations, in the 1960s and '70s used four-man rotations — or, perhaps more specifically, four-day rotations. The top pitchers pitched every fourth day, three days of rest. The Mets used a five-day rotation. Seaver's 35 starts in 1969 break down thusly: 18 starts on four days rest; eight starts on three days; four starts on five days; three starts on six days; and one start on two days (he made a one-out relief appearance and started two days later; it was four days after his previous start.) The Mets spaced out starts more than the other teams of the era did, which is why they never had anybody throw 300 innings in a time when that was not unusual.
Seaver, Ryan, Gentry and Koosman were all power pitchers. Jim McAndrew was not. McAndrew, age 25, started 21 games for the '69 Mets (and had six relief appearances) for 135 innings. His BFP worked out to 24.4, but it was skewed. He had starts in the first half of the season in which he faced 9, 6, 12 and 16 hitters. But in his last 11 starts, he never faced fewer than 25 batters, and once reached 41 (he pitched 11 innings). He was pitching well in August and September, and manager Gil Hodges rode him hard.
And like Gentry, he was washed up at a young age.