There are currently no old-age specific interventions for autistic adults. Therefore, in this explorative study, we examined the possible effects of a co-designed psychoeducation program for older autistic adults (55+ years), with a multiple case study design (N = 9, age 56-73 years; Netherlands Trial Register (code Trial NL5670)). For each participant, also a person close to them (a proxy) participated. This allowed us to calculate a discrepancy score regarding autistic traits and cognitive challenges. The main hypothesis was that our program, delivered after general psychoeducation, would result in a discrepancy reduction between self and proxy reports. However, contrary to our hypothesis, we observed neither intervention effects on our primary outcome measures (discrepancy scores) nor the secondary outcome measures (mastery, self-efficacy, self-esteem, self-stigmatization, quality of life, and hope and future perspectives). Thus, despite co-designing the current intervention, the results were not promising. However, the positive feedback and suggestions of the participants make developing an improved version of a specific psychoeducation program for older autistic adults still a worthwhile pursuit.