That depends on the type of guitar you have. Steel strings aren't going to be that rough on his fingers. Anything he plays will come with some amount of pain, but it really isn't much at all. And it certainly won't HURT your fingers. If you have a classical guitar, stick to nylon strings. If you have a steel string acoustic, stick to steel strings. Otherwise, you can actually do some damage to the guitar by stringing it different materials.
The difference in materials results in a vast difference in tension of the strings. This difference can often result in a neck becoming bowed, or, in extreme cases, cracking in the guitar, especially on the top above the soundhole. Whatever the guitar came with, stick to that. He'll be just fine. =)