Your male's growth rate sounds similar to my cb guy Rigel. I got him at 14 grams in early November '04 and he was pushing 180 when I last weighed him a few weeks back. My wc female, however, is growing at a much much slower rate. She was 35 grams when I got her back in August '04 and is now probably somewhere between 80 and 90 grams (she's pretty skittish so she doesn't get handled / weighed as often as Rigel).
8 is young. There's a chuck in the herp room where I attended college who is still going strong and is at least 14 years old. Some people I've talked to have mentioned that egg binding can be an issue in some females. I have no idea about maximum life expectancy. I know Tom Greb mentioned he lost a chuck at 13 to a mouth infection and felt that it was a premature demise.
If you get a chance, post some pics of your guys ;o)
Alice