Just buy brake fluid tester and test your self. that is the best indicator, very cheap in shopee/lazada. Really depends on how and where your drive, if always drive in area which is high in humidity like seaside, side river the brake fluid tester i tested 1 year also fail already and need change, some driven on normal roads around 2 years before showing fail in the tester. Do take note, Malaysia consider very high humidity country as we got rain most of the time and by logic it is way faster than the manufacturer recommendation date (usually 2 years or 20k) to change. The brake fluid tester test the water moisture in the brake fluid, if water moisture detected over certain % it will declare as fail and need to change.