I received a bulletin from my health insurance company a while ago, in which they stated that doctors had recently discovered that there were two particularly good ways to keep your mind sharp in retirement. One was to learn a foreign language, and the other was to learn a musical instrument. The first method is fine as long as you have someone close to you who speaks that language, thus allowing you the opportunity to practice your skills. If not, a musical instrument might be preferable because it does not require that you have a partner, in order to practice. Studies have also shown that children who are taught musical instruments tend to have much higher scores in math, than children who do not have that experience.
Playing an instrument is also one of the best forms of physical therapy available, if you suffer any type of injury to your hand. The musician must place his or her finger in exactly the right place, at exactly the right time, in order to produce notes which sound right. This requires that the musician develop a much more precise degree of fine motor control than what is required to simply squeeze a rubber ball.
Whatever instrument you choose to learn, depends on your interests and tastes. I have a bias toward the mandolin family, obviously, but there are legitimate reasons for my bias. Here they are:
1) In general, stringed instruments that have frets (mandolin family, guitar, and banjo) are a little easier to play than stringed instruments without frets (violin family). Fretted instruments are designed so that, if you place your finger anywhere on the string between two given frets, you will produce a reasonably accurate note. Instruments without frets require that you place your finger in exactly the right spot on the string, every time. And anyone who has ever heard a beginning violin student play, knows what happens when those fingers don't hit the exact spot. So, fretted instruments are quite forgiving because you can put your finger down in one spot to play a note, and, when you go back to play the same identical note, you can put your finger down in a different spot. And as long as you don't cross the fret, you'll still get the same note, and both will be reasonably accurate.
2) Among the fretted instruments, the mandolin family, in my opinion, is the one that has the most logical design. In order to play a basic scale, beginning players do not need to use any more than three fingers! They start by plucking the open bottom string (using no fingers). Then they press their index finger to the string, and pluck it. Then they press their middle finger to the string, and pluck it. Then they press their ring finger to the string, and pluck it. Then they move over to the next open string, and repeat the exact same steps. So in order to play a complete scale using all of the strings, the player would use the following sequence: 0 (open string), 1 (first finger), 2 (middle finger), 3 (ring finger), switch string, 0, 1, 2, 3, switch string, 0, 1, 2, 3, switch string, 0, 1, 2. In my opinion, that’s easier to play than a guitar, because the standard guitar tuning prevents you from playing a scale in order like that.
3) The instruments of the mandolin family fit just about every style of music imaginable - including classical, jazz, swing, New Age, bluegrass, Celtic, Caribbean and Eastern European. And, in many different cultures, there are instruments which are very similar to those in the mandolin family. So, no matter what your personal taste in music, an instrument from the mandolin family will sound quite nice. Examples of these different styles can be heard in the audio portion of this site.
4) Mandolins are used to play both rhythm and melody, which means that you can learn as little as you want, or as much as you want. If you can master about a dozen basic chords, you will know about 90% of what you need to play rhythm on the mandolin, at any jam session. Learning melody is a little more complicated, and, depending on your interests, can be a lifelong pursuit – as one musician said, "so many tunes, so little time….."
5) This might be stating the obvious, but mandolins are smaller than guitars. And if you ever tried to play the guitar and found it cumbersome to handle and to play because of your own body size, you might find a mandolin easier to work with.
Last but not least - many people are not aware that the mandolin family of instruments closely parallels the violin family. That means that someone who has experience in playing the violin, for example, can usually pick up a mandolin and play it very well, immediately, because the strings are tuned exactly the same - G, D, A, E. The difference is that the violin family has one of each string, and the mandolin family has two of each string. That also means that someone who has experience in playing the viola, would probably find it easier to play a different instrument in the mandolin family, called a mandola. They are somewhat bigger than mandolins and, because they are tuned exactly like a viola - C, G, D, A - they produce a richer, deeper tone than a mandolin. They are, however, played exactly like a mandolin. And someone who has experience in playing the cello, would find it relatively easy to play the mandocello. The mandocello is larger than a mandola, and is tuned exactly like a cello - C, G, D, A. The mandocello is also played like a mandolin, but produces an even deeper sound. So if you have prior experience with any instrument in the violin family, it would take very little effort for you to become proficient on the equivalent instrument in the mandolin family. The left hand fingerings are exactly the same, so all you would need to do is learn how to use a pick instead of a bow.