2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/2964I propose and apply a method for deriving ages of the metal-poor globular clusters (GCs) in a distance-independent way, which is based on age indicator related to the main sequence in the two-color diagrams with U-B index. Age of the metal-poor GC NGC 6397 has been estimated, using Yale isochrones of Demarque et al. (1996), to be close to 16 Gyr provided the cluster metallicity is near [Fe/H]=-2.0.2 pages, 1 figure, uses IAU207_pasp.sty (included). To be published in the Proceedings of the IAU Symposium 207, "Extragalactic Star Clusters", eds. E.K. Grebel, D. Geisler and D. MinnitiAstrophysicstext