What is the average reading age for a year 7?

It really depends on the person, and how much they've learned. IQ's are more accurate for adults whom have completed school. Each IQ test is different as well, making it difficult to make a positive answer. However, i'd say between 90-120.

Addendum:

If you seek a number for an IQ, then the "average" will depend on the test or instrument used. The most reliable and valid tests of IQ use a scoring and statistical procedure the places "normal" IQ between 85 and 115, with dead center at 100. Those numbers are a range of normal, representing a low end and a high end. Psychologists have developed useful tests for children as young as three years, on up through young adults. Testing the intellectual power of mature adults does not usually result in useful data.

Theories of "intelligence" are varied and complex, and most psychologists warn against using a single number or a single measure as more than the most general hint.