Abstract Growth dynamics helps to elucidate demographic aspects, such as age at specific size and size at maturity or first reproduction, which are important for sea turtle management. The Mexican Caribbean Sea is an important feeding ground for green turtles, but demographic data for the turtles are lacking. Size-based growth rates of immature green turtles inhabiting a foraging ground at Akumal Bay (20°24′0″N and 87°19′16″W) were obtained by using a mixed longitudinal sampling design from historic mark–recapture data (2004–2014). Curved carapace length (CCL) of immature turtles at first capture ranged from 27.8–81.0 cm and minimum size at recruitment was 27.8 cm CCL. Recapture intervals ranged from 1 to 49 months, 72% of the recaptures (n = 172) occurred in less than a year and 90% before 1.5 years. A monotonic size-specific growth function displays the maximum growth rate (6.25 cm yr− 1) at about 46–48 cm CCL before starts declining steadily at > 60 cm CCL. Mean size presented a non-linear relationship with growth rates and year of capture had a negative linear effect over growth; the lowest annual mean growth rates were registered during 2009 and 2012. Based on GAM predictions an immature sea turtle recruited to the feeding ground (28 cm CCL) would require between 13 and 14 years to reach the average nesting size, supporting field observations. A negative linear relationship between annual mean growth rate and the relative estimated sea turtle abundance (p = 0.001) suggests a density-dependent effect. The quantitative information presented will help understand life history patterns and provide a baseline to assess future dynamics of this green turtle population.