It is because the uai, is a rank of how (ready u are for uni) so they would have a certain limit as to where they can accept ppl, as a person who is in 50s they may not see as being ready for that particular course.... for example myself i got a uai of 57.85, i applied to a bachelor of science in information technology course at uts, but did not get in as it says that my qualifications arent sufficient for that course which the uai needed for that course is 80 something i beleive, but i did get into bachelor of information technology at uws which i needed a uai of 70 or more, this is because i had a partial done tafe course which i added through the supplementary form B, which was attached to the uac book........ so really all this is how ready u are for uni, not how good u went in the hsc, cause that is a one of mark....thats why they base uai, on all the marks through year 12 and hsc, as its more appropriate to how ready u are for uni.... not how good u are compared to others... (did i just confuse everyone??)