This somewhat depends upon just how old you are. When I was 26, I loved an eighteen-year old, and although we had a strong connection, the age difference proved to be too much. Now I'm much, much older, and my sweetheart is fourteen years younger than me, and it hasn't been and won't be a problem for us.
For an interesting take on this issue, check out a new film called Liberal Arts. Josh Radnor is 35, and he meets, and has a strong connection with, a 19-year old Elizabeth Olsen. As their characters are drawn on the screen, they are almost perfect for each other, if not for the age difference. In some ways, she is more mature than he is, and in the end, she helps him grow up. And no, nothing creepy happens between them.