Do I need to put premium gas if on the car it says premium only?

So I have a 95 infiniti j30 and on the dashboard it says "premium unleaded fuel only" but my bf says I don't need to put the most expensive gas because its an old car? like he's saying you only put it for newer cars? So now I'm confused do I need to put that type of gas or not? I just had the car for a couple of days and it has a pretty big engine it only gets 16 mpg.