Thats how we were brought up in our family. My older cousin is around 13 months older than me and i call her apa, my younger sister is only 11 months younger than me and she calls me baji and my younger cousin brother who is like 12 months younger than her calls her aapi.
wow u lucky gall
ma sis is 7 yrs younger than me and she says "ABC idher aaooo"
but i kinda like ittt