Thinking Power and IQ decrease with Aging??

As we age our brains shrink in volume, especially in the frontal cortex. The volume of the brain decreases by about 5% every 10 years from about the age 40. Memory also declines. However, that does not necessarily mean that older people will suffer reduced performance in certain cognitive tasks as they get older. They may, for example, compensate to some extent by enhanced experience. And the rate of physical brain decline after age 40 varies from person to person and is probably affected by lifestyle and diet. Use it or lose it is the key!

I agree with Mr @corum that, thinking power and IQ decreases with aging,  varies from person to person.

age is inversly proportional to IQ. but that does not mean that an older person cannot play chess.

it seems that you get slower, but also sharper. see last years St Louis games Kasparov played. his positions was better than his opponents in nearly every game still time was his biggest problem.