For Olga Nikolayevna, I think I read somewhere that during captivity (during which she was very distraught and worried) it certainly did appear that she had aged, looking like a "middle-aged woman", if I'm remembering correctly.
In my opinion, on each of their parents' side, the aging seemed okay (I think Ella, Alix's sister, aged extremely well), but sometimes they did look much older than what they really were. I don't know how well the girls and Alexei would have aged (probably well, in my personal opinion), but, considering that it was highly possible that the Grand Duchesses also carried the haemophilia gene like their mother and therefore likely to pass it on to their sons, could have caused intense grief and stress for them, perhaps also making them age very quickly, like their mother had, especially during the terrible Spala incident in 1912 (who, already within a number of days, noticeably aged, also with white hair beginning to appear).
And exactly like Sarushka, Janet and AnastasiaExpert said, smoking could have also caused aging, had the children survived.