Can someone explain this sentence from the intro? > To remove stars with unusually high and precise ages, we require old stars to be metal-poor and α-enriched.

Can someone explain this sentence from the intro? > To remove stars with unusually high and precise ages, we require old stars to be metal-poor and α-enriched. Particularly, why remove stars "with unusually ... precise ages"? Why does increased precision decrease plausibility/accuracy?