Although researchers have found strong relationships between first language (L1) skills and second language (L2) anxiety, less is known about how L1 skills in primary school impact L2 anxiety years after L1 has been acquired. Previous research lacked evidence for the mediating role of L2 aptitude and L2 achievement in the relationship. This study applies structural equation modelling to examine pathways by which L1 skills are associated with L2 anxiety via the mediators. Sixty-five students were administered L1 skill measures from 1st-5th grades, then followed over 10 years when completing L2 courses in high school. We examined the model across six different ages and found the effect of L1 skills on L2 anxiety was indirect through L2 aptitude and L2 achievement, indicating the impact is better understood through the mediators. The effect of L2 achievement on L2 anxiety is direct, and large in magnitude. Results remained stable across different ages and invariant across gender.