Although evidence on aspects of individual ageing of LGBTQI (lesbian, gay, bisexual, transgender, queer and/or intersex) people is mounting, there is a poor understanding of the macro aspects of population ageing within the LGBTQI population itself. This paper seeks to address this lacuna through an examination of structural and numerical ageing of the Australian LGBQ population. Drawing upon new data sources, alongside recent advances in demographic modelling, we utilised a modified multi-state cohort-component projection model to produce estimates and projections of the ageing of the Australian LGBQ population from 2016 to 2041. Our results indicate that the LGBQ population is significantly younger than the heterosexual population and is ageing structurally (in relative terms) at a slower rate. However, the LGBQ population is ageing considerably faster numerically (in absolute percentage growth terms) relative to the heterosexual population. We show the LGBQ population aged 65+ is projected to grow between 150 and 170 per cent between 2016 and 2041, under relatively conservative assumptions. This strong numerical ageing counters traditional assumptions about ageing of the LGBQ population and provides data to improve visibility of this population and to ameliorate future planning for health, care and social service provision that is appropriate and well-funded. The methods and materials we develop in this paper provide new opportunities for other countries to improve planning for LGBQ populations similarly.