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We present a new method to estimate the absolute ages of stellar systems.This method is based on the difference in magnitude between the main sequenceturn-off (MSTO) and a well defined knee located along the lower main sequence(MSK). This feature is caused by the collisionally induced absorption ofmolecular hydrogen and it can be easily identified in near-infrared (NIR) andin optical-NIR color-magnitude diagrams of stellar systems. We took advantageof deep and accurate NIR images collected with the Multi-Conjugate AdaptiveOptics Demonstrator temporarily available on the Very Large Telescope and ofoptical images collected with the Advanced Camera for Surveys Wide Field Cameraon the Hubble Space Telescope and with ground-based telescopes to estimate theabsolute age of the globular NGC3201 using both the MSTO and theDelta(MSTO-MSK). We have adopted a new set of cluster isochrones and we foundthat the absolute ages based on the two methods agree to within one sigma.However, the errors of the ages based on the Delta(MSTO-MSK) method arepotentially more than a factor of two smaller, since they are not affected byuncertainties in cluster distance or reddening.Current isochrones appear topredict slightly bluer (~0.05mag) NIR and optical-NIR colors than observed formagnitudes fainter than the MSK.

On a new Near-Infrared method to estimate the absolute ages of star clusters: NGC3201 as a first test case