Females that are fat also have a very increased risk of egg-binding and death, as well as throwing slugs, throwing small clutches, etc.

You can't just say that only the small, underweight females have this risk. I only had 3 females lay clutches this year. One is an 02-03 and is probably over 5 feet, but yet she was only 2600g at the beginning of the season. She was a bit thin in my opinion, but she laid 7 perfectly calcified, big eggs in June and is 250g away from her original before-breeding weight right now. Heaven forbid she only gets 4-5 medium mice a week.
My other female is barely 4 feet but is 2300g. She's a bit overweight(YES, she only gets 3-4 mice a week and is a chunky butt) and while her eggs were big, they weren't as nicely calcified as the other female's, and the surface of the eggs were a bit bumpy(hatchlings were smaller too).
The last female was a rescue who I considered underweight, and is an 03 or 04 and was around 1500-1600 when I first got her. She gave 5 perfectly calcified, albeit small, eggs. 3 of the babies are huge now and 2 are still around 35-45g.

What if you had a female that was just a small build? Say an 03 who was 1000-1200g? If she's healthy and has adequate fat reserves for her size, then why not? Not every snake is going to make it to 1500g.

And SnakieMom: NO, she's not old enough. See how heavy she is at 3 years old. Also.. Wait until she hits that teenage angst age(around 1100-1200g), then see how well she grows. She's definitely not going to be ready to breed at only a year old.