Well, he did ask about what depth to which he is "certified."
Rather embarrassing, I would think, for SSI, that he did not know this.
I also doubt that SSI covers various gas mixes in their basic open water class. So unfortunately he does not know what the choices are nor what the training progression normally is. I have to wonder if anyone even mentioned even nitrox to him.
But it is good that he is thinking about it now, with C-card in hand.
EAN 32 is a popular mix, and it is quite safe to 130 ft. Whether the diver diving with nitrox to 130 ft can handle the narcosis at 130 ft is a different story, of course. I have found that narcosis on air or nitrox is not really debilitation until about 150 ft, but that is a different topic.
Suffice it to say, this SSI diver is "certified" to about 75 ft since he is certified for air.