Castilla,

Any guitar store with an "in-house" repairman will answer your question quickly although clansfolk has given you excellent guidelines. A 30 year old guitar is not an "old" guitar if it has been treated well. The greatest evils are temperature and humidity (especially humidity). They can lead to problems with the finish and to cracking of the wood. Cracks are most likely to appear aong the grain of the top, sides, and back. Most guitar stores sell humidifiers (for 10 to 15 dollars, American) you can place in the guitar or case to keep the proper humidity. As for temperature, if you are comfortable in that temperature (in your shirt sleeves) the guitar will be comfortable. Freezing porches and steaming hot car interiors can be a problem.

A well made guitar is not especially at 30 years. I have two guitars over 30 that I play. I have suffered more from those 30 years than the guitars have.

It is imperative that you get the right answer about steel versus nylon strings. Nylon strings place much less tension on the guitar and so they can be build "lighter". Steel strings will eventually cause serious damage to the nylon string guitar. My one personal experience (an error of youth) led to the bridge being ripped right off the face of the guitar. If the guitar is meant to have steel strings, it will enjoy them better than nylon, and they will sound better with steel strings.

May your son and you, enjoy the guitar.

Roger in Baltimore