How much can the average 30-year-old bench press?
If by average you mean a mostly sedentary individual weighing about 165lb? In the region of 119lb for a single rep.
It depends on the average male. Some can bench-press more weight than others, depending on their pectoral, biceps and back-muscle strength they have. Some can bench-press as much as 300 lbs; others may only be able to bench-press only around 100 lbs. Just like there are many different body types of each man, there are different levels of strength that each and every individual 21 y.o. man has.