This dataset provides groundwater ages estimates that were used in an assessment of the penetration depth of modern groundwater in the Central Valley aquifer system (CVAL). Groundwater ages were estimated by calibration of environmental tracers (tritium, tritiogenic helium-3, chlorofluorocarbons, sulfur hexafluoride, carbon-14 and radiogenic helium-4) to lumped parameter models (LPMs) for samples from 650 sample locations. Groundwater samples were collected from wells (mainly drinking-water) in the CVAL between 2004 and 2017 as part of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP) and the National Water-Quality Assessment (NAWQA) Project. Table 1 reports the primary results of this assessment including mean groundwater age and the input for calculation of mean groundwater age: results of the tritium age classification, condensed results from dissolved gas modeling, and calculated environmental tracer concentrations. Calibrated lumped parameter models provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages that explain the measured tracer concentrations in a sample. Tables 2, 3, and 4 provide results in support of Table 1. Table 2 reports detailed results for the calibration of dissolved gas models to neon, argon, krypton, xenon, and nitrogen. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas (mainly from denitrification) that explain the measured dissolved gases in a sample. Table 3 reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results in Table 2. Calculated concentrations of environmental tracers that can be used in groundwater age calculations are the dry air mixing ratio of sulfur hexafluoride or chlorofluorocarbons, tritiogenic helium-3, which is the concentration of helium-3 from the decay of tritium, and radiogenic helium-4. Table 4 reports information used to calculate the partial exponential model ratios used in the groundwater age modeling. In addition to these four tables, two ancillary tables are included to provide more detailed information about the fields and the abbreviations used in tables 1-4.