I was 17 when I went to univ, and the disadvantage for me was that I couldn't go to pub during orientation. There was a classmate who was over 21 at that time, and the advantage for him was that he could rent car cheaper, so ppl always invited him to long trip. You don't really have to tell people about your age, so it's really how you see it yourself.
Most people still have to take university courses to enchance their career after they have graduated from first degree, so by that time, everyone is over 22.