From the wikipedia article:
The finding of rising heritability with age is counterintuitive; it is reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. However, that the opposite occurs is well documented. According to work by Robert Plomin,[7] heritability estimates calculated on infant samples are as low as 20%, rising to around 40% in middle childhood, and ultimately as high as 80% in adult samples in the United States. This suggests that the underlying genes actually express themselves by affecting a person's predisposition to build, learn, and develop mental abilities throughout the lifespan.
Note that the infant samples are low (20%), and then rise with age. One interpretation is the one suggested in the article, that the genes express themselves by affecting the person's predisposition. The other is that the 20% is the actual genetic content, and the increase comes from the environment provided by the parents.
Read up on how much IQ can be improved by studying (for instance, taking course on writing the GRE). Read up on how much IQ is affected by nutrician. IQ is much like strength - it responds to training, diet etc. Take two children, feed one properly and give them plenty of exercise, while feeding the other lots of simple carbs and let them watch TV all day and the conclusion you'll come to is that the first kid is genetically stronger and healthier ...