In all honesty, this is really important at all ages, but even more so as we age and lose some of our physical strength and prowess. One of the secrets of generating high levels of power in Karate is by using the natural elasticity of the muscles (rather than the forced contraction of them). A small change in our approach can make a big difference; giving you a lot more power for less effort. This is especially important as we get older and out bodies become less able.
If this video interests you, then on my Youtube channel, there is a full module on Relaxed Power, which I would suggest you check out.