The person in question also looks like she’s in her early 20’s. She had a chronic condition where she was basically in a waking coma but wasn’t “experiencing” stuff for a decade so it’s as if time had jumped from her POV because she has no memories of that period.
This gap is so disorienting for her that she identifies her age as 22. Being told her actual birth year causes confusion and distress, as it clashes with her sense of time and personal experience.
Not necessarily weird. I’m part of social groups where the youngest are in their mid or early 20s and the oldest are in their 70s or early 80s. If there are common interests it can work. Though I do get why this can be side-eyed if the older parties exclusively only hang around younger people.