Jimminy! So much of what you're describing could have been in my family. I was the eldest and was what my mother euphemistically described as "well endowed," short and plump with red-gold hair laying in waves down my back. My nearest in age sister (18 months younger) was ash-blonde, bony thin, and always tall for her age. I was bookish and she was flirtatious. We were and still are complete opposites.