4 years or 6-7 feet and THICK for females. Don't worry about the males, they'll breed if they want to and size doesn't mean a damn thing. As for live-bearing being less of a headache than eggs, think again my friend. I've done both and let me tell you, I'd rather have the repsonsibility in my hands and have fertile eggs than a giant unknown sitting in a captive female boa's abdomen! With eggs, all the guesswork has already been worked out for us by the pioneers of the industry! All the temps, humidties, incubation lengths, and lay dates are already worked out for 99% of the species! All the hard work is done! Hatching eggs is 1000x times easier than getting live babies from a boa.
...and I wish you the best of luck!