O-2 - PSR J1614-2230 is an old evolved system with characteristic age 5.2 Gyr
The recycled state (full spin-up, low eccentricity 1.3e-6, evolved WD companion) independently attests to a Gyr-scale binary evolution history: the proposed formation channel involves an original ~3 Msun companion star and predicts the neutron star accreted only a few hundredths of a solar mass, implying it was likely born massive (~1.9 Msun) and has held essentially this mass for its whole life.
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Why this is evidence
A concrete, independently dated instance of the class the neutron-star bound needs: a massive neutron star that has persisted for gigayears with a long-lived binary companion (the companion providing the beam-dump exposure that circumvents magnetic screening on the production side). Its survival is expected under H-22 and improbable under H-8-type fast-accretion physics applied to a hole captured in supranuclear-density matter, where accretion is fastest of all. Same discrimination direction as the general neutron-star-population observation, from a distinct measurement.