AstraZenaca does pose a greater risk of blood clotting for younger guys aged between 20 to 40 based on international experience and statistics so far particularly female. Also its protection is much smaller than Pfizer/BioNTech particularly to the notorious Indian strain and British strain. Even UK now recommends British residents under 40 to take Pfizer/BioNTech.
In Australia, even with limiting AstraZenaca to people aged 50 and above, the statistics so far is about 1 in 60,000 chance of getting the blood clot problem which is not a minor side effect.
Whether it is a wise choice to sign a waiver for those below 50 in order to get a COVID 19 shot earlier is of course a risk and benefits consideration for the particular person in question.