Inclusive education (IE) refers to the education of all learners, with or without disabilities, irrespective of their status or origin, who share the same learning spaces. IE is a multidimensional approach based on rights and quality of life paradigms. As teachers are agents of change, they must have the knowledge and competencies to meet this challenge. This study aimed to find potential associations between teachers’ preparation and their age and years of teaching experience. A cross-sectional study with a sample of 1275 teachers working in early childhood, primary and secondary education was performed. They answered three dichotomic questions about their initial and ongoing preparation and The Evaluation of Teacher Preparation for Inclusion (CEFI-R) Questionnaire. The dichotomic questions showed that 26.4% of respondents felt qualified to face the challenges of their students’ diversity. There were significant inverse associations between the CEFI-R Dimension 1 (diversity conception), Dimension 3 (supports), and Dimension 4 (community participation) and the teachers’ age and years of teaching experience. This means that the higher the age or the years of experience, the teachers’ perceived preparation for inclusion is worse, which should encourage us to take measures to improve teachers’ competencies and preparedness.