Oh yes, I find I fear the thought of immortality too.
I must agree we change so much that apart of us dies... Not just through the development growth as you state "coming of age" part of you defiantly "dies" here but also through trauma and other experiences.
So other than the normal growing and changing that I went through being a girl, I could say I've change /died on top of this another 3 times. And one of those deaths I can say was a complete change.. I do not see any part of my old self in me any more, from physically to morally to mentally. This death was due to illness and emotional change.
The concept of death is fluid, it doesn't just apply to the physical body and it can be viewed as a positive..