I have a stepson and stepdaughter; Mr. Kitty and I married when they were nearly-10 and 11 respectively. I had no hand in their raising- actively went out of my way to avoid such a thing, actually, as Mr. Kitty and the ex had things in hand- but 12.5 years later I refer to them as my stepkids for expedience’s sake (“stepson-in-law” is a mouthful, though).
A coworker married her husband when his daughter was grown; she has had fairly consistent contact with her since the wedding (dad was involved throughout the daughter’s childhood, so it wasn’t a case of absenteeism) and uses the term stepdaughter.