Went to doc for sinus infection. abdominal exam revealed "palpable abdominal aorta" & now told to get ultrasound. but a bit young for possible aaa???

Pulsatile mass: yes. typically AAA is found in a much older individual unless you have connective tissue disease such as Marfan syndrome. With regards to the work up, I believe a CT scan is a much better exam and more conclusive if the test is being ordered to investigate a possible AAA. Also, if AAA is suspected, pressing on the abdomen with the US transducer may not be a good idea.

It is possible: to have an AAA but not likely it is prudent to be thorough with a palpable abdominal aorta. If you are very thin that is not unusual however if the Aortic palpation reveals an expansile aorta it is more worrisome