Giving an instrument from a relative or friend a second life might save you some money, when it does not have the appropriate size it will lead to many frustrations along the learning path or worse: an abrupt stop to guitar lessons.
Having the correct guitar size is crucial in developing a proper posture and playing technique in order to avoid injuries. Most nylon string guitar brands (Yamaha, Cordoba, Alhambra, ...) offer several different guitar size models.
A meet up at a local music store to have the student 'feel' the comfort and difference of a 'right-sized guitar' is usually convincing enough. (I personally have all guitar sizes at my home studio to experiment with, when considering an upgrade in guitar size for one of my students).
Guitars for Kids
Although there are small size steel string guitars, too often young players are suffering from pain in the left hand fingertips because of the much thinner steel strings. These guitars also have a larger body and might be a struggle for a younger student to find a proper posture.
Nylon String Guitars have a wider neck with more room for left hand fingers and due to wider string width, the right hand finger-picking / plucking style benefits as well.
Guitars for Adolescents and Adults
Fewer problems occur with older students or adults. Adjusting the footstool, using a guitar cushion or ergoplay for posture, playing a smaller size guitar, or use low-tension strings might help overcome certain playing difficulties.
Looking at the neck of the guitar, you 'll notice that frets (the space between the little metal strips) are getting smaller in higher positions. For this reason some instructors might use a 'capo' to shorten the neck. Although this might be easier on the left hand, the body size remains the same.
Because of this, younger players (-12 years old) will suffer from an incorrect right hand position which results in a bad posture. Bad posture equals: lower back problems, neck pain, tension while playing, bad technique, ... The capo-solution could be used temporarily for kids that recently switched to a full guitar size to make the transition smoother, but caution is advised.
Importance of Listening to your Body
Use a mirror and observe your own playing. Make sure your instrument is adjusted to you, instead of having your body adjusted to your instrument. It all starts with the correct guitar size.
Every body is built differently (let's not even talk about hand size and nail shape), therefore often posture and technique can be a very personal thing. Inform your instructor about the signals you are getting from your body. He or she can guide you towards a direction that will avoid discomfort during playing, so you can concentrate on what really matters: the music!
It's one thing to copy famous players' posture or technique, but usually, if it doesn't feel right, something needs to be adjusted until it does.
Purchasing a Guitar
Because guitars are mainly made out of wood, and no trees are equal, no instruments sound or play the same either. Not even when they have the same model number or brand name.
Therefore, it is highly recommended to let your instructor try out several guitars for you in your price range before making the final decision.
If you are planning on buying guitars online, be sure to check on the return policy and reputation of the business. An instrument could arrive damaged due to shipping or temperature fluctuations.
(click on the links next to the scaled guitar picture to purchase recommended brands and models)