If he does not mind the scheme of the bike and it fits, sure why not. Terry as you likely know is a female specific brand (at least it was last time I heard).
I normally am not an extreme color scheme person but I know how important it can be to a 7 year old.
You can get decent bikes for cheaper. 4'6" sounds tall for a 7 year old (I don't have a chart handy or remember how tall mine is). I am not sure if a 20" or 24" will fit him (wheel size). If a 24" will do then check out forum member Dirt Devil. He has a sweet 24" that any boy or mountain biking parent would like for $300. I would think you would be able to find something new for $350 or less. That is what the 20" at least were going for at Performance as recently as Dec. I did not check the 24" prices. Fit should be the first factor in whatever choice you make.