1. He is of average height.

Question

2. He is around average height.
3. He is a little below average height.
4. He is over average height.
5. He is of much more average height.
6. he is a little average in height.
7. He is more average in height.

(Are they all grammatical?)

Answer 1

1 - 4 are OK. I wouldn't use the others.