Im 18 and the guy I want to date is 29. Hes also my boss at my work. My work doesn't have a relationship policy but just to not let it interfere with work. But is it legal since I am 18?

First In the US, there is no dating laws what so ever, there are laws that effect if you can have sex. At 18 you are free to make all the mistakes you want.

You are old enough to date him, but to date your boss is in my opinion a foolish thing to do, and pretty dumb on his part to date someone one he holds authority over especially since you are not even out of your teens.
But like Chuck just said you are free to make all the mistakes you want.