When do girls all start to grow breast buds?

Girls puberty. Puberty in girls starts around age 8-9 with hair on lower legs usually first, getting taller next, breast buds next and typically last is pubic hair although that varies. This can all take a few years and some are slower to develp than others. Normal would be first needing a bra from age 9 to 15. Monthly cycles can be normal to start in those age ranges also.
Wide range. You expect to see emergence of one budding on one or both sides between 8 & 13.(2nd side will catch up ) Failure to see any budding by 13 and or menses by 16 would warrant a workup for pubertal delay.