As the popular saying goes - "You can't teach an old dog new tricks", but what does it actually mean? In the saying, the old dog is a metaphor for somebody old, saying that as they get older it becomes harder to learn new things. Apparently there is point in time when the brain becomes too plastic to learn new skills, and this plasticity increases with age. You might have come across this in some way, when you encounter someone old who finds it difficult to take on board new concepts - for example new technology - or is too stubborn or uninterested to change their old habits. Instead of using new technology, and for instance using a computer word processor, they will use an old typewriter instead. What about middle aged people, who are not interested in taking up a new hobby or learning a new sport, saying that it is too late now to start, and that they never would have been good at it anyway. This saying alludes to the times you see grumpy bitter old men, and you think to yourself don't bother them, they are too old to change their ways.
Upon first consideration there are truths to this statement, especially in the physical sense. As we get older we become physically less able, which makes us less inclined to learn new sports, or we lose our hearing, making us less inclined to learn to play an instrument, or our hearts become weaker, making us less inclined to do strenuous activities and exercise, or our emotions diminish, giving not enough passion or fervour to create and discover like we used to. These examples support the idea that when we become old, our ability to learn new things diminishes because we have passed our prime.
However, when we look more closely at this issue, there are many things that reveal many of these considerations to be unrelated to age. It cannot be denied that as you get older you will find things more difficult to learn, but this is not simply a reduction in ability, and a great deal of it is weighted on the state of mind of the individual. As previously stated, stubbornness makes people unwilling to try and learn new things, which is often mistaken for being unable to learn new things. In other words, the problem is highly psychological, since being stubborn is a state of mind, and something that can develop and become reinforced with someone as they get older. So, while it is unfortunately true that aging is naturally linked to physical bodily decline, this only puts restrictions on the most strenuous of sports and physical activity. Even so, there are plenty of examples of older people who keep themselves in shape throughout earlier life and find that they can still do the physical things that they did when they were young. This leads to the point that the individual will always be the exception to the rule of the masses, and so no-body should be misled into thinking that they cannot perform when they get older just because it apparently happens on average. Take obese children or people with serious illness, diabetes and so on - if you are lucky enough not to have been affected by such health problems in life, then you should certainly make the most of what you have got anyway, whether you are old or young.
Mental decline is true with aging also, but there is no clear or quantifiable relationship between age and mental ability, or progression of age and the decline of mental ability. Again, everybody is different, and the real limitations that people face are the restrictions set by one. Being afraid to learn for fear of judgement or mockery, or being afraid of failure are such limitations, and these bring on an unwillingness or even a physical inability to learn new things and adapt to new situations, making improvement impossible.
Having made these considerations, it would now be appropriate to change the original saying "You can't teach an old dog new tricks" by changing the word "old" with the word "stubborn" or "cowardly".
Someone who is old is not confined to what he or she can do because of their age, but rather the external conditions that arise because of their age. Some people are not confined by such conditions, and it is common for middle aged and older people to do the things that younger people are usually associated with doing, such as travelling around the world, sky-diving, bungee jumping and so on. Likewise it is also common for people who are not affinitive with such excitement to take up new hobbies, and take up new interests in new academic fields, long after their children have graduated and started having children of their own.
People have the power and the potential inside of them to decide on their own whether or not they want to learn something new. Age is simply a number humans use to define how many years we have been present on planet Earth, and people should not feel constricted by this number just because of the influence of society which amounts to little in the long run. You can let this number grind you down and make you more negative, but this in turn will decrease the opportunities that open themselves up to you, as your feelings have an impact on the world around you. Or you can simply see this number as a number, and live each day as a new day, in a world where there are things to be discovered for everyone. As long as the desire to learn and develop continues, being able to learn new things will continue right up until the end of life, which is much better than giving up whilst you're still alive. Many college professors and academics stay involved in their work for their entire lives, with famous examples such as Einstein still trying to unify and expand our knowledge right up until his final days on Earth. Is there any wonder that such people were able to stay so mentally active and ready to learn new things right into old age, when there is scientific proof that links mental ability and plenty of mental practise? The same applies to those who love sports, with older people still experimenting and doing new sporting activities for as long as they are physically able.
The "Old Dog" metaphor is a very prevalent metaphor, though I believe it is a very misguided metaphor. It is a shame that older people can often be discouraged to learn or do new things when they feel intimidated by younger people, but this is something that must be overcome. As is common not just for old people but young people, it is the fear of failing that stops them for trying in the first place, or being ridiculed by other people in case they make mistakes or do not perform. Indeed the vast majority of issues presented are not at all related to age, but the individual and society at large, and the societal perception of older people being of less use than younger people. The most important thing to realize is that as long as we are alive, we will be learning and trying new things, and if this process is stopped due to uncertainty or doubt, then older people need to realize that they need to get over these trivial concerns if they want to make as happy for themselves as possible. We can learn from older people, but older people can learn from us too, no matter how old they are.