Can someone in their 20s already have an aortic aneurysm?

Aneurysm: It is possible, could be thoracic or abdominal.Please get an ultrasound exam asap.

Rare: Most are caused by long-standing high BP and smoking. However, there are connective-tissue diseases and congenital defects that can show up. These are often thoracic (in chest) and may involve the aortic valve. In patients at risk -with marfan's or the like- echocardiogram or other imaging may be indicated.

Very rare: Only if they have a rare collagen vascular disease like marfans.