One ‘reasonable ground’ for unlawful sex with a minor is mistaken age. Alcohol consumption and make-up are often deemed further influences on impaired perception. Two hundred and forty persons in bars and cafes rated the attractiveness of composite faces of immature and mature females with and without additional make-up, alcohol users having their concurrent blood–alcohol level measured using a breathalyser. A non-sex-specific preference for immature faces over sexually mature faces was found. Alcohol and make-up did not inflate attractiveness ratings in immature faces. While alcohol consumption significantly inflated attractiveness ratings for participants viewing made-up sexually mature faces, greater alcohol consumption itself did not lead to overestimation of age. Although alcohol limited the processing of maturity cues in female observers, it had no effect on the age perceptions of males viewing female faces, suggesting male mate preferences are not easily disrupted. Participants consistently overestimated the age of sexually immature- and sexually mature-faces by an average of 3.5 years. Our study suggests that even heavy alcohol consumption does not interfere with age-perception tasks in men, so is not of itself an excuse for apparent mistaken age in cases of unlawful sex with a minor.