Legally no, although you may find your interests and maturity levels to be significantly different.
I have found guys that age and older who date women that young do so because they find it easy to manipulate them. Women that young are just not experienced enough to even see it happening. They find the attention flattering and mistake it for love.
If you think about how much one matures between 16 and 18, it is the same from 18 to 21, and then again from 21 to 25. By the time someone is 28 they should be not be interested in someone who is 18. They should feel the person is not mature enough for them. With that in mind the only reason to date someone that young would be to use or manipulate them.