There has been little international research looking at differences in mental health across different age groups. This study examines mental health inequities between transgender people and the Aotearoa/New Zealand general population from youth to older adulthood. The 2018 Counting Ourselves survey (N = 1178) assessed participants’ mental health using the Kessler Psychological Distress Scale (K10) and diagnoses of depression and anxiety disorders, questions that were the same as those used in the New Zealand Health Survey. Our results showed significant mean score differences for transgender people on K10, and these differences were almost two standard deviations higher than the general population (Cohen’s d = 1.87). The effect size differences, however, decreased from youth to older adults. Regression analyses indicated trans women were less likely to report psychological distress than trans men and non-binary participants. There was an interaction effect for age and gender, with lower psychological distress scores found for younger trans women but higher scores for older trans women. The stark mental health inequities faced by transgender people, especially youth, demonstrate an urgent need to improve the mental health and wellbeing of this population by implementing inclusive institutional practices to protect them from gender minority stress.