How many calories should you consume if you are 20 and weigh 180 pounds?

I see nobody else will touch this one. It depends on how tall you are and how active. The average 20 year old that is moderately active is somewhere in the 2000 calorie range.

If you want to maintain weight somewhere between 1600-2200 is a good range depending on how active you are and how fast you metabolism is. If you are trying to lose weight I wouldn't go below 1200 and would try to hover around 1600 and get more excersize. Again, depending on your metabolism. It might be more important where those calories come from, than how many there are. If you are getting your 4-6 fruits and veggies (go heavier on the veggies) 2-3 protein and 6-11 whole grains you are getting enough to eat. I have trouble eating all that in a day myself and I cannot imagine eating all that and still having room for junk. Anyway, if you weight is steady then however many you are eating is enough to maintain that weight at you present activity level.