Does your IQ increase with age or does it degrade with age? and what is the use of having IQ results?
IQ is relative to other people of your age and typically does not change as you age.
Your IQ results give some indication of how smart you are. Or at least how good your abstract logic is. A result of 125 means you're "smarter" than 95% of the people of your age. There's no real reason why an employer would need to do IQ tests though, especially not multiple ones, unless they're really worried about cognitive decline.
