It was still unclear how homocysteine (Hcy) levels and cognitive deficits change in patients with schizophrenia of various ages. The present article attempts to assess the relationship between Hcy levels and cognitive deficits in patients with schizophrenia across age groups, especially in young people. Totals of 103 patients and 122 healthy controls were included. All participants were stratified into four groups according to their age: 18-29 years, 30-39 years, 40-49 years, and 50-59 years. Clinical data, plasma Hcy levels, and cognitive function score were collected. Cognitive function was evaluated using the MATRICS Consensus Cognitive Battery of tests assessing speed of processing, verbal learning and memory, visual learning and memory, working memory, and attention/vigilance. Compared with the healthy group, Hcy levels increased significantly, and all the measured cognitive function score were significantly lower in all age groups of patients with schizophrenia (p < 0.001). Hcy levels were negatively associated with speed of processing (SoP), working memory (WM), and visual learning and memory (Vis Lrng) score in 18-29 years. Further multiple regression analysis showed that SoP were independently associated with Hcy levels in patients with schizophrenia aged 18-29 years (B = 0.74, t = 3.12, p = 0.008). Based on our results, patients with schizophrenia performed worse on cognitive assessments and Hcy levels were more closely related to cognition in young patients.