Aims To evaluate the associations of parental reproductive age with the risk of myopia and high myopia in adult offspring. Methods This cross-sectional study included 14 044 UK Biobank participants. Myopia and high myopia were defined as a mean spherical equivalent (spherical power+1/2 cylindrical power) of both eyes ≤−0.5 dioptres (D), and ≤−6.0 D, respectively. Parental age was categorised as <25, 25–29, 30–34 and ≥35 years. Logistic regression was conducted after adjusting for age, sex, race, time spent outdoors, Townsend Index, income, education, body mass index, smoking and drinking. Interaction terms between parental age and outdoor activity were further added to the logistic regression models. Results The prevalence of myopia and high myopia among adult offspring generally increased with parental reproductive age. Logistic regression analysis revealed that advanced maternal age significantly increased the risk of myopia and high myopia. Maternal age over 35 years was associated with the highest risk of myopia (OR, 1.42; p<0.001) and high myopia (OR, 1.56; p=0.029). However, no significant effect was observed for advanced paternal age on the risk of myopia and high myopia. Interaction analysis indicated that compared with spending 0–2 hours outdoors daily, more than 2 hours attenuated the effect of maternal age on progression of myopic refractive error. Conclusion Advanced maternal reproductive age had a detrimental effect on the risk of myopia and high myopia in offspring, which could be mitigated by engaging in daily outdoor activity.