I'll be 30 in Febuary, just finished my first semester.
Had a cracking time in all honesty. If your friendly, open and most importantly, talk down to the 18 year olds, you'll be fine. My age has never been an issue once.
As for the whole, "Is it right to date an 18 year old" debate, it very much depends on the people involved. There's 18 year olds on my course I wouldn't just to sharpen a pencil whilst there's others who've really got their lives in order. It's not my place to judge people, especially on something so arbitary as age