Would it be considered illegal for me, a 16 year old to be dating and having sex with an 18 year old, in New York?

As of 2003 no -- but law might have changed since then -- Savage
Statutory Rape Laws by State (http://www.cga.ct.gov/2003/olrdata/jud/rpt/2003-R-0376.htm)

According to my information it would be considered statutory rape still.

Take a look at this website: New York - Age of Consent (http://www.ageofconsent.com/newyork.htm)

It seems that it is okay since you are within 4 years of each other, and you are not under 14.