He may get a little bigger yet. One of mine stopped growing at 7 months and the other at 11 months. The type of shampoo and conditioner you use can make a big difference. I use minksheeen shampoo and pantene conditioner. I usually leave the pantene on for ten minutes before rinsing. This leaves their hair silky smooth and tangle free. Here is a link to the minksheen
http://www.touchofmink.com/prod_details.asp?id=15