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 [less than or equal to]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.