Introduction: Each year, around 600 young (<40 years) breast cancer (BC) patients are registered in the national NABON Breast Cancer Audit (NBCA). The aim of this study is to compare patient and treatment characteristics of young and older age BC patients over time with a focus on outcome of quality indicators (QIs). Furthermore, we analysed whether de-escalation trends of treatment can be recognized to the same degree in both patient groups. Material and methods: From October 2011 to October 2020 all patients treated for stage I-III invasive BC were included. Tumour characteristics, treatment variables and outcome of QIs of two age categories young (<40 years) and older patient (≥40 years) were analysed. Results: In total 114,700 patients were included: 4.6% young patients and 95.4% older patients. Young patients more often presented with a palpable mass, higher stage, and triple-negative BC. Overall, young patients more often started with neoadjuvant systemic treatment (NST) (54.3% vs. 18.6%) and a greater proportion of the young patients retained their breast contour after surgery (73.5% vs. 69.3%). De-escalation trends such as decrease in axillary lymph node dissections and in the use of boost were observed. The omission of radiation treatment after breast conserving surgery was only observed in older patients. Conclusion: Although this study shows that young women more often present with unfavourable tumours, therapeutic procedures are performed with a higher adherence to the QIs than for older patients and young women do benefit from some de-escalation trends to the same extend as older patients.