if you are singapore citizen holding pink IC, pls note the minimum to enter the profession is 26, this is a agreement with republic of singapore air force with the government, it is stipulated in civil aviation regulations, there is no such thing as serving them longer, there are people inside SIA that are previously doctors, dentists, lawyers, economists which have worked many yrs outside before joining them.
you can have myopia 500 but if your visual acuity is more than 6/60 unaid then pardon to say you are out.
i know of ppl with 400 but visual acuity more than 6/60. it really depends how man rows of letter you can see the snellen chart without your spectales. i m having 450 but visual acuity just nice 6/60 unaid.
but if you are trying for airforce pilot application, you will just need 500 and below for both eye.
but one thing i m very sure, you must have 5 O level passes in one sitting with english, maths, science plus your 2A 2AO or diploma or degree and more than 1.65m in height as i have seen people sent off by SIA HR home before the interview as these information are not captured during your online applicaiton.
hope all is clear...