You can always compare how little has Hiyori changed in those 100 years, to how much have kid Gin, kid Matsumoto, kid Hisagi, kid Nanachan, the kid Scientist-Akon, young teen Byakuya have grown.
Hitsugaya isn't old himself, he is the youngest Captain class fighter after Ichigo.
Renji's and Rukia's situation, where they change in 10 years from 6-9 year old kids to 16-19 teens (from the looks of it) is probably the best example of that, especially seeing how like in the next 50 years they barely change.
Kid Gin too seems that have changed in those in 9 years to a teen (his height changes from kid Hisagi's to teen Byakuya's).
@paul, from what I can tell, Byakuya is around 125 years old, Hisagi is 108 years old, Nanao is 107 years old, Matsumoto and Gin are around 118 and alike.