Background: Both nature exposure and green exercise (GE) provide numerous health benefits. However, there are no studies examining the impact of childhood GE on adult health. Methods: 45 healthy adults (aged 69.8 ± 8.4 years) took part in the study, wearing a Firstbeat heart rate variability (HRV) monitor for 24 hours. Participants also completed questionnaires assessing childhood and adulthood nature exposure and GE, as well as current connectedness to nature (CN), perceived stress and well-being. Pearson’s correlations and linear regression were used to examine relationships between variables. Results: Childhood nature exposure and GE significantly predicted adult nature exposure and GE (β .317, p < 0.05) as well as CN (β = .831, p < 0.01). After controlling for childhood nature exposure and GE, CN was negatively associated with the percentage of stress over the 24-hour period (r = −.363; p < 0.05) and positively associated with HRV during sleep (r = .415; p < 0.05). Conclusions: CN is important for adult health; however childhood nature exposure and GE are essential to developing this connection.