If I were sixteen, I would not go below fifteen. As for higher, I would not go higher than eighteen.
I say that I will not go lower than a year less only because it gets creepy to date people that are young when you are already in high school. It might not matter as much later in life, but at sixteen, you are a young adult - able to drive and looking foward to only two more years of high school - and dating someone more than a year younger at this time involves you with someone who still has years left, and is in a different world, a different mindset, with problems that you cannot relate to. While you worry about prom and passing finals, they are worried about acne flares.
I say that one should not go over eighteen for a similar reason, only in this case you are the younger one. You are still worried about grades and tests. You are probably living with your parents, and maybe starting up a job. Older than eighteen, you are dealing with someone that could be in colledge. They might be living alone, already with a steady job. They are done with school if they choose to, and there is even legal matters due to the difference in age.
Anyway, that is my thoughts on the subject. Like I said, the range of dating grows as you get older - as the differences in daily life is not as dependent on age - and at that point you can focus a bit more on finding someone, rather than multi-tasking with school and such. In short, at 16 I would date 15 to 18.
