Contrary to popular armchair psychology, there is no significant evidence that IQ and age are inversely related. In general, however, the older we get, the less we use our brain, and it becomes like a muscle that we no longer use.
Contrary to popular belief there is no sound evidence for believing many of the claims made for IQ tests. IQ measures ones ability to do IQ tests and little else. They were originally invented as a means of measuring the response of mentally defective patients so that their progress under different treatment regimes could be compared. There is no evidence to support the many claims made that IQ measures "innate" intelligence. If you practice IQ tests your score will increase. When I was 10 I used to spend each Friday afternoon practicing IQ tests for the entry examination to the upper school. My "IQ" increased by 30 points over that time, an most of the people in the class managed to improve their score by at least 10.
The point: Yes, you can improve your brain, and you can take proactive steps to increase your IQ.
Absolutely, it may not be the best idea if you want to be able to fit in socially however. You will then have to leave in a world where everyone you meet has a lower IQ. Phill