Age as a function of stellar mass for known CO-rich debris systems. As in Fig. 7, the red symbols indicate disks with estimated CO masses >0.01 M_⊕, while the orange ones represent disks with M_CO between 0.001 and 0.01 M_⊕. The labels of the disks (numbers or letters) are also the same as in Fig. 7. The solid green and dashed blue curves show the lifetimes of primordial gas in disks depleted in submicron size dust particles assuming initial disk masses of M_disk,0 = 0.1M_* and M_disk,0 = 0.03M_*, respectively. The curves are taken from Ooyama et al. (2025).