Yes, dosages vary by your size, weight, gender, stress, and other factors. Part of type 2 diabetes is often insulin resistance, but people with type 1 can also suffer from it as well (although it's not the cause of type 1). Some people even need to use highly concentrated forms of insulin, ie U-500 instead of the standard U-100.

Body weight is a huge factor, so what is fine for an adult can kill a child. There are a lot of factors at work here that influence this so there is no easy answer as to what is a 'safe dose'.