Between 1990 and 2012, the global mean age at diagnosis of autism spectrum disorder ranged from 38 to 120 months. Measures have since been introduced to reduce the age at autism spectrum disorder diagnosis, but the current global mean age is unknown. This review and meta-analysis report the average age at diagnosis from studies published between 2012 and 2019. We initially identified 1150 articles, including 56 studies that reported the mean or median age at diagnosis across 40 countries (n = 120,540 individuals with autism spectrum disorder). Meta-analysis results (on 35 studies, including 55 cohorts from 35 countries, n = 66,966 individuals with autism spectrum disorder) found a current mean age at diagnosis of 60.48 months (range: 30.90–234.57 months). The subgroup analysis for studies that only included children aged ⩽10 years (nine studies, including 26 cohorts from 23 countries, n = 18,134 children with autism spectrum disorder) showed a mean age at diagnosis of 43.18 months (range: 30.90–74.70 months). Numerous factors may influence age at diagnosis and were reported by 46 studies, often with conflicting or inconclusive findings. Our study is the first to ascertain the global average age at autism spectrum disorder diagnosis from a meta-analysis. Continued efforts to lower the average age at autism spectrum disorder diagnosis are needed. Lay abstract We currently assume that the global mean age at diagnosis of autism spectrum disorder ranges from 38 to 120 months. However, this range is based on studies from 1991 to 2012 and measures have since been introduced to reduce the age at autism spectrum disorder diagnosis. We performed a systematic review and meta-analysis (statistical analysis that combines the results of multiple scientific studies) for studies published between 2012 and 2019 to evaluate the current age at autism spectrum disorder diagnosis. We included 56 studies that reported the age at diagnosis for 40 countries (containing 120,540 individuals with autism spectrum disorder). Results showed the current mean age at diagnosis to be 60.48 months (range: 30.90–234.57 months) and 43.18 months (range: 30.90–74.70 months) for studies that only included children aged ⩽10 years. Numerous factors that may influence age at diagnosis (e.g. type of autism spectrum disorder diagnosis, additional diagnoses and gender) were reported by 46 studies, often with conflicting or inconclusive results. Our study is the first to determine the global average age at autism spectrum disorder diagnosis from a meta-analysis. Although progress is being made in the earlier detection of autism spectrum disorder, it requires our constant attention.