Background: Bipolar disorders (BD) figures on top of the World Health Organization classification of disabling disorders. It is unclear if there are socioeconomic, functioning, and cognition differences in young patients newly diagnosed with BD and whether these are different for young and adult patients newly diagnosed with BD. Understanding these differences is important for tailored treatment and support. Methods: Participant groups included 401 patients newly diagnosed with BD, 145 of their unaffected first-degree relatives (UR) and 209 healthy control individuals (HC). First, we compared socio-economic status, functioning and cognition between young patients newly diagnosed with BD (150), UR (61) and HC (92) (15–25 years) and adult patients newly diagnosed with BD (251), UR (84) and HC (117) (>25 years), respectively. Second, within patients, we compared functioning and cognition between young and adult patients newly diagnosed with BD. Results: In both participant groups, patients newly diagnosed with BD, and to a lesser degree UR, had lower socio-economic status and impaired functioning and cognition compared with HC. Further, young patients newly diagnosed with BD were less functionally impaired, than adults newly diagnosed with BD, whereas cognition did not differ between groups. Limitations: Applied tools for assessments of functioning and cognition are not validated below age 18. Conclusions: Overall, lower socio-economic status and impaired functioning and cognition were found both in young and adult patients newly diagnosed with BD and their UR compared with young and adult HC, respectively. Young patients were less functionally impaired than adults, but cognition was similarly impaired.