Eh biasanya around 6-9 bulan dah ada startle reflex yang obvious, tapi some babies mmg lebih sensitive! My first one was jumpy gila sampai like 1-2 tahun, my second one macam relax je Anak ke-4 mu tu mungkin personality dia just chill, atau maybe dia dah outgrow it na since dah besar sikit, setiap baby beda-beda lah, don't worry!