Pitching coach Jeremy Hefner thought almost all offseason about how to configure the Mets’ rotation. The average age of the team’s top five starting pitchers is 35. Their combined salary in 2022 is $129.3 million. How can the Mets keep them healthy throughout the six-month regular season, and if all goes according to plan, a month of postseason play as well?

Hefner pondered a six-man rotation. He pondered non-traditional alternatives such as openers and piggyback starters. But for now, at least through April, the Mets plan to rely solely on their big five — Justin Verlander (40 on Monday); Max Scherzer (39 in July); Carlos Carrasco (36 in March); José Quintana (34); and Japanese newcomer Kodai Senga (30).

The sturdiness of that group likely will determine the success of a team carrying a luxury-tax payroll of $373.7 million, about $80 million over the highest threshold — you know, the one the league ostensibly sought to slow down the spending of Mets owner Steve Cohen. The total outlay for the 2023 Mets currently projects to at least $450 million in combined salary and tax penalties, an unprecedented number. And still the team is hardly certain to win its first World Series since 1986, in part due to the age and injury risk in its rotation.

The Mets have a number of 30-and-under starters capable of filling in — David Peterson, Tylor Megill, Elieser Hernández, Joey Lucchesi. But if Verlander and/or Scherzer, in particular, fail to produce as expected, the Mets’ outlook will grow dimmer. Which is why Hefner and manager Buck Showalter are vowing to remain flexible with their rotation plans.